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ANIMAL PRODUCTION |
* Departments of Animal Science and
and
Statistics, University of Wyoming, Laramie 82071-3684
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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Key Words: Beef Cattle • Body Condition Score • Lipid Supplementation • Prepartum Energy Balance
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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). Cows maintained in a negative energy balance during the prepartum period were in poor body condition at parturition and had an extended period of postpartum anestrus (Hess et al., 2005). Dietary lipids have been hypothesized to be nutraceuticals (Williams and Stanko, 1999), acting as nutrient partitioning agents to shift energy use from one metabolic process to another (Bottger et al., 2002), thereby increasing the potential to maintain optimal BCS as the breeding season begins.
Although the inherent homeorhetic regulation involved with lactation makes repartitioning of nutrients away from the mammary gland difficult, provision of certain dietary fatty acids were associated with repartitioning of nutrients to support specific productive functions (McNamara et al., 1995; Bottger et al., 2002). For example, Bottger et al. (2002) attributed maintenance of greater body condition during lactation in beef cattle to supplementation with linoleic acid, whereas dietary oleic acid increased milk fat synthesis. Increasing the condition of thin lactating beef cows by repartitioning nutrients toward adipose tissue reserves rather than milk fat synthesis could lead to improved reproduction (Houghton et al., 1990b) and decreased maintenance requirements (Wagner et al., 1988).
We hypothesized that supplementation with oleic acid would increase milk production of above-average-conditioned beef cows, whereas supplementation of linoleic acid would increase palpable adipose tissue reserves of thin beef cows during early lactation. Therefore, our objective was to evaluate the interaction of BCS at parturition and supplementation of cracked high-oleic acid or high-linoleic acid safflower seeds on cow and calf production.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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) of 4 or 6 at parturition. In each year, the most uniform cows (n = 36/yr) within each group (BCS 4 ± 0.07; 479.3 ± 36.3 kg of initial BW and BCS 6 ± 0.07; 579.6 ± 53.1 kg of initial BW) were then used in an experiment for the first 60 d of lactation.
Cows assigned to obtain a BCS of 4 at parturition were managed to be in an energy-deficit state during the second trimester (November to January) and then were fed to meet maintenance requirements throughout the third trimester of gestation to ensure that post-partum cow and calf performance was not affected by a prepartum energy deficit during the third trimester. Average BCS of cows assigned to achieve a BCS of 4 at parturition was 4.8 early in the second trimester (November). During the second trimester, those cows grazed pastures with low forage availability. Using estimated energy balance (Mcal/d) derived from BCS change (NRC, 2000), pasture intake was estimated at 8.78 kg/d. Analysis of comparable pastures at the same facility has shown that the pasture was 6.9% CP and 56.5% TDN during the fall grazing period (Schleicher et al., 2001). During the third trimester, cows assigned to be BCS 4 at parturition were maintained in a drylot and fed (DM basis) 7.25 kg of bromegrass hay (8.5% CP) and 2.5 kg of dehydrated alfalfa pellets (17% CP) daily. Alfalfa pellets were provided to ensure that mammary immunoglobulin production and calf intestinal absorption would not be adversely affected because of maternal dietary protein intake (Quigley and Drewry, 1998).
Initial BCS of cows assigned to achieve a BCS of 6 at parturition was 5.4. Cows assigned to this group were fed to increase condition during both the second and third trimesters. During the second trimester, cows in the BCS 6 group grazed pastures similar to those for the BCS 4 group but with adequate forage availability. Estimated DMI based on performance during the second trimester was 10.9 kg of pasture/d. During the third trimester, cows were housed in a drylot and fed (DM basis) 9.4 kg of bromegrass hay (8.5% CP)/d and 3.0 kg of dehydrated beet pulp pellets (10.5% CP)/d.
Cows were assigned randomly within BCS group to postpartum dietary treatment as they calved. Beginning 3 d postpartum, cows were placed into one of six pens (six animals per pen) with individual feeding stanchions and were fed twice daily. Diets (DM basis) were hay (2.13% of BW during yr 1 and 2.03% of BW during yr 2) plus a low-fat control supplement (0.57% of BW during yr 1 and 0.30% of BW during yr 2) or supplements with either high-linoleate (hay at 2.32% of BW and supplement at 0.39% of BW during yr 1; hay at 2.03% of BW and supplement at 0.23% of BW during yr 2) or high-oleate cracked safflower seeds (hay at 2.32% of BW and supplement at 0.40% of BW during yr 1; hay at 2.03% of BW and supplement at 0.24% of BW during yr 2). Each treatment (BCS of 4 or 6 at parturition and dietary treatment) was represented in every pen with an average calving interval 
7 d within each pen. Previous research at the University of Wyoming indicated that cows of similar genetics produced 9 kg of milk during peak lactation (Bottger et al., 2002). Therefore, our diets were designed to meet the energy requirements of a 544-kg beef cow producing 9 kg of milk/d at peak lactation. Diets were formulated to provide equal quantities of N and TDN within each year (Table 1). Dietary ingredients were analyzed for CP (Leco FP-528; Leco Corp., St. Joseph, MO), IVDMD (Daisy II Incubator; Ankom Tech. Corp., Fairport, NY), crude fat (2050 Soxtec Avanti Auto Control Unit; Foss Tecator, Eden Prairie, MN), and fatty acids via direct transesterification (Whitney et al., 1999) with methanolic HCl (Murrieta et al., 2003). Dietary CP was greater in yr 2 because of differences in the hay used during yr 1 (bromegrass hay; 8.5% CP) vs. yr 2 (foxtail millet hay; 10.6% CP). Dietary TDN was similar between years, and lipid-supplemented diets were formulated to provide 5% of DMI as fat.
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Milk production was measured on d 30 and 60 of lactation. Beginning at 0500, each cow was separated from her calves, administered 20 USP of oxytocin i.m. (Vedco, Inc., St. Joseph, MO), and milked using a mechanical milking device; the remaining milk was hand-stripped. Cows were allowed 2 h to consume their rations, after which they were released from their individual feeding stanchions and given free access to water for an additional 2 h. After 4 h, cows were given a second i.m. injection of oxytocin (20 USP) and milked as previously described. Each cow’s 4-h milk output was extrapolated to total 24-h milk production. Calves were weighed at 0500 and returned to the cow immediately after the second milking. A sample (approximately 20 mL) of milk was sent to a commercial laboratory (Rocky Mountain DHIA, Logan, UT) and analyzed for total crude fat, CP, and lactose (lactose was analyzed only in yr 2). Beginning on d 65 postpartum, cows were implanted with an intravaginal controlled internal drug-releasing device (CIDR; Eazi-breed, Pfizer Animal Health, New York, NY) impregnated with 1.38 g of progesterone for 7 d. After removal of the CIDR, 25 mg of PGF2
(Lutalyse, Pfizer Animal Health) were injected i.m. Cows were bred by AI 12 h after detection of estrus. Cows were monitored for resumption of estrus and rebred by AI. After the second cycle of AI breeding, cows were commingled with bulls (one bull per 25 cows) for an additional 30 d. First service conception rate for synchronized first AI breeding was determined by monitoring recurrence of estrus and relative calving date. Overall pregnancy rate was determined in the fall by palpation per rectum, which was confirmed at the time of calving.
Statistical Analyses
Most data were analyzed by ANOVA as a 2 x 3 factorial arrangement of treatments (BCS at parturition and postpartum dietary treatment) in a randomized complete block design; year was the blocking factor, and cow was the experimental unit. Data collected at parturition or on d 3 postpartum were analyzed as initial observations to ensure that data collected once the postpartum dietary treatments were imposed did not require covariate adjustment. A repeated measures design was used to determine the effect of BCS at parturition and postpartum diet over time (e.g., d 3 to 30 and d 30 to 60) on cow and calf performance. The appropriate correlation structure was used for repeated measurements conducted on each cow-calf unit to obtain valid statistical inferences (Littell et al., 2000). For repeated measures on body characteristics, likelihood ratio testing suggested an autoregressive (AR-1) correlation structure, and for measures on milk production, the correlation among observations on each cow was accounted for by treating cow as a random effect. The following statistical model was analyzed via the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC):
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where i = 1,2(BCS); j = 1,2,3(Diet); k = 1,2(Year) l = 1 to 72(Cow); m = 1,2,3(Day PP), and yijklm denotes the value of a body characteristic or milk production variable of interest on day m for cow l within year k assigned to the dietary treatment j and having BCS i; µ + i + ßj + ( ß)ij + 
k + 
m + ( )im + (ß)jm denotes the mean production variable for year k, BCS i, diet j, and day m, containing the effects for BCS ( i), diet (ßj), the inter-action of BCS and diet ( ß)ij, day (m), the interaction of day and BCS ( )im, and the interaction of day and diet (ß)jm; and 
l(ijk) represents the random effect associated with cow l in year k with BCS i and diet j. 
ijklm denotes residual errors. The effects i through (ß)jm comprising the mean response were considered as fixed and were included in the MODEL statement. The random effect of cow within year, BCS, and dietary treatment (specified in the RANDOM statement) accounted for the correlations among repeated observations on the same cow. The REPEATED statement was used to specify the AR-1 correlation structure for the residual errors (ijklm). Data that were not collected each year were analyzed as repeated measures in a completely randomized design rather than a randomized complete block design.
Interactive effects of BCS x dietary treatment were generally not detected (P = 0.18 to 0.98). Consequently, our discussion focused primarily on the main effects of BCS at parturition and dietary treatment. During the first year of the study, one calf died; however, the cow was mechanically milked twice daily to enable her to stay on the experiment. Observations from this cow were tested for normality (PROC UNIVARIATE) to ensure that her observations were not outliers. During the second year of the study, one cow-calf pair was removed from the study because of the death of the calf. Necropsies performed at the Wyoming State Veterinary Laboratory revealed death of calves from both years were due to complications not attributable to the study; consequently, comparisons of main effects and interactions were determined using least squares means. Pearson correlations also were conducted to evaluate relationships among variables for production traits.
Breeding data were analyzed with STAT Xact with Cytel Studio (Cytel statistical software, Cambridge, MA) using Zelen’s exact test for homogeneity of odds ratios (Zelen, 1971; Breslow, 1981) to properly evaluate the binary distribution of dichotomous responses (i.e., the cow was either successfully bred or it was not successfully bred). The odds ratio (OR) was computed as follows (where Prob. = probability):
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Note that when the probability of breeding was 1, the probability of not breeding was zero, which results in an undefined expression. In situations when an estimated probability was 1, there was no upper bound on the confidence limit. Lower bounds >1 imply a significant difference between the two groups.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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indicated that BCS at parturition is a major determinant of length of postpartum anestrus; cows in optimal (BCS 5; Wagner et al., 1988) to nearly optimal condition have a shorter period of postpartum anestrus than do cows in suboptimal condition. Body condition score is an indicator of energy reserves in the form of lean muscle and/or adipose tissue that may be used to support physiological processes during times of increased metabolic demands. A target BCS of 5 to 6 (1 = emaciated to 9 = obese; Wagner et al., 1988) was suggested as optimal for cows at parturition to ensure adequate postpartum performance (Lamond, 1970; Dziuk and Bellows, 1983; Morrison et al., 1999). Nonetheless, plane of nutrition or energy balance as parturition approaches was suggested as an important factor affecting postpartum reproductive performance (Houghton et al., 1990b). In a recent review, Hess et al. (2005) noted that cows were often maintained in a state of negative energy balance prepartum to achieve a suboptimal BCS at parturition. Evaluating energy balance prepartum and BCS at parturition together may help explain postpartum production results attributed to BCS at parturition. Therefore, prepartum energy balance in the current study was estimated to determine the effect of energy balance at differing stages of gestation on postpartum performance.
In the current study, energy associated with change in BCS during the prepartum period was determined by estimating the change in BW that occurred at a given BCS (NRC, 2000). The validity of these estimates was supported by comparison of predicted and actual performance, where performance predicted from NRC (2000) suggested that cows would lose 1 BCS in 143 d, whereas actual performance was a 0.5 decrease in BCS within 70 d (Table 2). During the third trimester, the NRC (2000) predicted that cows would lose 1 BCS in 256 d, whereas actual performance resulted in a decrease of 0.3 BCS in an average of 70 d.
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Moderate feed restriction during the second trimester, followed by additional feed during the third trimester of gestation, may be an effective management strategy for improving use of resources in a forage-based system without affecting calf birth weight (Freetly et al., 2000). Nonetheless, the influence of cow energy balance and BCS at parturition on postpartum performance should be considered when making managerial decisions.
Effects of Cow Body Condition Score at Parturition on Cow and Calf Performance
A BCS at parturition x day of lactation interaction was detected (P = 0.04) for change in cow BW (data not shown). Cows with a BCS of 4 lost similar BW from d 0 to 30 compared with d 30 to 60 (6.3 to 5.5 kg), whereas cows with a BCS of 6 at parturition lost more BW from d 30 to 60 compared with d 0 to 30 (5.3 to 15.4 kg). Initial BW of cows in BCS 4 was less (P < 0.001) than cows in BCS 6 (Table 3). The 96-kg difference in BW of cows between the two BCS groups was within 16 kg of the predicted BW change of a 483-kg cow in BCS 4 changing to BCS 6 (NRC, 2000). Cows in BCS 4 at parturition were able to maintain (P = 0.02) BCS throughout the 60-d postpartum feeding trial, whereas cows in BCS 6 lost condition. Molle et al. (2004) observed decreased visceral organ mass of cows experiencing nutrient restriction (1.07 Mcal/d below maintenance) during early gestation, which may lower maintenance requirement per unit of metabolic BW (Houghton et al., 1990a). Therefore, the apparent improved efficiency of cows in BCS 4 could be partially explained by an overall improvement in nutrient use caused by a decreased maintenance requirement as a result of decreased visceral organ mass (Hess et al., 2005).
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). Ultrasonography may provide an improved method to objectively estimate fat and muscle change in live cattle. Ultrasound measures were taken in the current study to compare palpable BCS to a quantifiable measurement. In a review, Williams (2001) indicated carcass and ultrasound measures were highly correlated. Research from our laboratory with mature cows indicated that actual LM area and 12th rib fat were correlated (r = 0.49 and 0.85, respectively) with ultrasonic measurements (Miller et al., 2004). As expected, ultrasound measurements of 12th rib fat and LM area were less (P < 0.001) for cows in BCS 4 than for cows within BCS 6 at parturition. No difference was detected for 12th rib fat change (P = 0.18) or LM area change (P = 0.67) because of BCS. A BCS at parturition x day of lactation interaction was detected (P = 0.05) for LM area. Cows in BCS 4 had an increase (P = 0.04) in LM area from d 30 to 60 (41.3 to 46.5 cm2), whereas cows in BCS 6 had similar (P = 0.51) LM area from d 30 to 60 (65.8 to 62.5 cm2). Body condition score at parturition was correlated (P < 0.001) with 12th rib fat (r = 0.87), LM area (r = 0.64), and BW (r = 0.75) at d 3 of lactation. These relationships were also evident at d 30 and 60 of lactation.
Cow BCS at parturition did not affect 24-h milk production (P = 0.71), milk fat percentage (P = 0.53), 24-h milk fat output (P = 0.41), 24-h milk protein output (P = 0.19), milk lactose percentage (P = 0.70), 24-h milk lactose output (P = 0.44), milk energy per kilogram (P = 0.54), or 24-h milk energy output (P = 0.52). Cows in BCS 6 had greater (P = 0.03) milk protein percentage than cows in a BCS of 4. McNamara et al. (2003) also reported increased protein content of milk from dairy cows in better condition and fed greater dietary energy before parturition. Those researchers attributed this response of augmented milk protein content to increased availability of tissues used for mobilization in cows maintained with greater energy reserves. Lack of change in BCS for cows in BCS 4 in the current study suggests that these cows mobilized less tissue than cows in BCS 6. Similarly, the BCS at parturition x day of sampling interaction for change in LM area supports the concept that lean tissue mobilization for milk protein synthesis is contingent on the status of energy reserves.
Because slightly thin- to moderate-conditioned cows could be maintained on lower-quality feed and return to estrus within an acceptable time following parturition (Lemenager et al., 1980; Houghton et al., 1990b), it could be suggested that profit potential may be improved by avoiding over-conditioned cows. Houghton et al. (1990b) reported that thinner cows had a longer period of postpartum anestrus, but also reported cows in suboptimal condition at parturition that were increasing BCS had greater first-service conception rates than fleshy cows with a decreasing BCS. A BCS at parturition x dietary treatment interaction (P = 0.02) was detected for overall pregnancy rate (Figure 1). Cows managed to achieve a BCS of 6 at parturition supplemented with the control and high-linoleate safflower seeds had 100% overall pregnancy rates; however, cows supplemented with high-oleate safflower seeds tended to have lower (66.7%; P = 0.09) overall pregnancy rates than either cows fed control or high-linoleate supplements. Overall pregnancy rate for cows managed to achieve a BCS of 4 at parturition did not differ (P 
0.22) across dietary treatments. Bottger et al. (2002) attributed increased milk fat in cows supplemented with oleate to a decrease in BCS of cows at d 90 of lactation. Perhaps a residual effect occurred in the current study, where cows in BCS 6 and supplemented with oleate partitioned nutrients toward milk fat leading to a negative energy balance beyond peak lactation (after supplementation ceased). Unfortunately, no measures of BCS or milk production were taken beyond d 60 of lactation to support this hypothesis.
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). Therefore, the apparent improved efficiency for cows in BCS 4 was not sufficient to elicit an increase in reproductive performance. Lamond (1970) proposed the idea of a target BCS at parturition to ensure optimal postpartum performance. Dziuk and Bellows (1983) further suggested a minimum BCS of 5 would permit adequate body energy reserves for acceptable postpartum reproductive performance. Morrison et al. (1999) substantiated this concept by indicating that prepartum nutrition during the last trimester did not influence postpartum reproductive performance as long as cows were within a BCS range of 5 to 6. Results from our study support the contention of a target BCS, where despite improved efficiency of cows in BCS 4 during the 60-d postpartum period, bodily energy reserves were insufficient to obtain desirable reproductive performance.
Calf birth weight (P = 0.83) was not influenced by cow BCS at parturition (Table 3); however, combined BW of calves at d 30 and 60 tended (P = 0.09) to be greater for calves nursing cows with BCS of 6. Wiltbank et al. (1965) suggested that cows consuming low-energy diets during the last trimester could adversely affect calf survivability and performance. Similarly, Houghton et al. (1990b) reported decreased calf birth weights from cows fed at 70% of NRC requirements (Mcal/d of NEm) compared with cows fed at maintenance. Energy balance calculated from reported (Houghton et al., 1990a) cow performance indicated that those cows were 2.54 Mcal/d deficient during the third trimester. Additionally, BCS of cows fed to 70% NRC were 4.6 at parturition (converted to a nine-point scale), whereas cows fed at maintenance were in BCS 5.9 at parturition. Although cows in the current study and that of Houghton et al. (1990a) were in similar BCS, the thinner cows in the Houghton et al. (1990a) study were nearly 4.5 times more deficient in energy during the third trimester than were the cows in BCS 4 in the current study. Hough et al. (1990) also reported no difference in birth weight of calves from cows restricted by an estimated 1.74 Mcal of NEm/d prepartum compared with cows fed at 100% NRC requirements for energy and protein. The energy balance of cows in BCS 4 in the current study was –0.59 Mcal of NEm/d during the last trimester. Cows in the current study fed slightly less than maintenance (BCS 4) during the third trimester had similar calf birth weights as cows fed above maintenance. Collectively, these results suggest that energy balance of cows during the last trimester is of greater importance for calf birth weight than actual cow BCS at parturition.
Body condition score at parturition in the current study did not affect (P = 0.48) calf ADG. This finding agrees with the results of Houghton et al. (1990b), who, despite previously mentioned differences in birth weights, observed no differences in calf ADG through d 60 caused by prepartum nutrition. DeRouen et al. (1994) also reported that variation in prepartum BCS and BW change associated with level of nutrition did not influence calf ADG or weaning weight. Results from the current study demonstrate that calf performance will not be affected negatively by cow BCS at parturition, as long as energy and protein intake is near maintenance during both the last trimester and during the postpartum period. Calf ADG from d 30 to 60 was correlated (P = 0.002; r = 0.36) with 60-d milk yield. Similarly, calf BW at d 60 was correlated (P = 0.002; r = 0.37) with 24-h milk energy output at d 60. This relationship between calf ADG and milk energy agrees with the results of Brown and Brown (2002), who reported a significant relationship between calf ADG and milk fat. The relationship between milk energy and milk fat percentage is well established (NRC, 2000); therefore, the relationship between calf ADG and milk energy in the current study was not unexpected.
Effects of Dietary Treatment on Cow and Calf Performance
Dietary treatment did not affect BCS change (P = 0.94) or BW change (P = 0.27; Table 4). Similarly, no differences were noted for 12th rib fat (P = 0.24), change in 12th rib fat (P = 0.69), LM area (P = 0.21), or change in LM area (P = 0.96). Given the lack of production responses caused by dietary treatment, the lack of difference in ultrasonic measures was not unexpected. De Fries et al. (1998) also reported that lipid supplements did not influence BW of cows during the early postpartum period. In contrast, however, those researchers reported an increase in BCS through an increase in adipose reserves in cows fed lipid supplements.
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; Drackley and Schingoethe, 1986). Our results agree with others who have reported that dietary lipid supplementation does not influence milk fat percentage (Eastridge et al., 1988; Komaragiri et al., 1998) or total milk yield (Komaragiri et al., 1998; Bottger et al., 2002). Through homeorhetic regulatory functions, the endocrine system may supersede dietary influences on nutrient partitioning to support specific metabolic activities (Komaragiri et al., 1998). Therefore, the nutrient demands of lactation might have superseded any partitioning effect caused by specific fatty acids. Nonetheless, the lack of dietary treatment effect on productivity by beef cows in the current study was unexpected because previous research by our laboratory (Bottger et al., 2002) suggested that partitioning of nutrients was influenced by type of fatty acid supplementation. Apparent repartitioning effects of oilseed supplementation were detected at 90 d of lactation in the study of Bottger et al. (2002). Peak milk production in beef cows occurs at about 60 d (NRC, 2000). Perhaps the nutrient demands associated with early lactation masked potential partitioning effects associated with lipid supplementation during the first 60 d of lactation. Alternatively, lack of differences in production would be expected because all diets provided equal N and energy. Thus, our results indicate that specific fatty acids in dietary lipid supplements may not be effective repartitioning agents during early lactation.
First-service conception (P = 0.56) and overall pregnancy rates (P = 0.55) were not affected by dietary treatment. Similarly, Bottger et al. (2002) reported no differences in postpartum interval or number of days to conception because of lipid supplementation of similar diets in primiparous heifers. In a compilation and analysis of results obtained from refereed literature, Hess et al. (2005) concluded that first-service conception and overall pregnancy rates were not affected by feeding fat to postpartum beef cows.
No differences were detected for calf birth weight (P = 0.24), ADG (P = 0.81), or overall calf BW (P = 0.44; Table 4). The only interaction detected for calf production traits was a BCS at parturition x dietary treatment x day of sampling effect (P = 0.05) for calf ADG. Calves nursing linoleate-supplemented cows in BCS 6 had a greater (P = 0.05) ADG between d 30 and 60 than calves nursing linoleate-supplemented cows in BCS 4 (1.0 vs. 0.77 ± 0.09 kg) between d 30 and 60. Additionally, calves of oleate-supplemented cows with BCS 6 had a greater (P = 0.01) ADG from birth to d 30 than from d 30 to 60 (1.02 vs. 0.78 ± 0.08 kg). Results from previous research conducted at the University of Wyoming (Bottger et al., 2002) and elsewhere (Tjardes et al., 1998) also found no difference in calf performance because of lipid supplementation; however, De Fries et al. (1998) attributed increased ADG of calves suckling cows supplemented rice bran to a potential increase in milk energy. The overall lack of calf performance in the current study would be expected because milk energy output was not affected by lipid supplementation.
Effects of Day of Lactation on Cow and Calf Performance
Because of an average gestation of 281 d in Angus cattle (Aiello, 1998), a cow must be rebred within 84 d to maintain a yearly calving interval. Resumption of estrus by d 60 postpartum is essential for cows to have at least two opportunities to be bred by d 84 postpartum (Dunn and Moss, 1992; Hess et al., 2005). Houghton et al. (1990b) suggested that cows must be in moderate to nearly moderate condition at parturition to resume estrus within 60 d postpartum. Similarly, Richards et al. (1986) observed increased estrual activity within 60 d postpartum when cows were in moderate to optimal condition (BCS = 5 to 6) at parturition. Therefore, in the current study, d 60 postpartum was targeted as the time when effects caused by either BCS at parturition or dietary lipid supplementation during lactation would need to have occurred to maintain a yearly calving interval.
Cows lost (P = 0.01) condition by d 30 but not between d 30 and 60; however, cows tended (P = 0.08) to lose BW between d 30 and 60 (Table 5). No differences were detected for cow BCS (P = 0.40), 12th rib fat (P = 0.53), change in 12th rib fat (P = 0.83), LM area (P = 0.30), or change in LM area (P = 0.39) because of day of sampling.
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). Because the relationship of milk fat and milk energy are highly correlated (McDonald et al., 2002), a decrease in milk energy concentration was expected as milk fat decreased.
Milk protein percentage reflects the relationship between protein yield and milk yield (DePeters and Cant, 1992). Increased lactose content leads to an increase in osmolarity, thereby increasing overall milk yield and decreasing protein percentage. This relationship is supported by a negative correlation between milk lactose and milk protein percentage at d 30 (P = 0.02; r = –0.41) and d 60 (P < 0.001; r = –0.87) in yr 2 of the current study.
No differences were detected for ADG (P = 0.18) between d 3 to 30 and d 30 to 60; however, as expected, calf BW was greater (P < 0.001) at d 60 than at d 30 (Table 5). Beal et al. (1990) reported a positive relationship between milk fat and preweaning ADG. A positive correlation (P 0.002) was noted between calf ADG and 24-h milk energy output at both d 30 (r = 0.41) and d 60 (r = 0.38). Additionally, average (d 30 and 60) milk energy yield was positively correlated (P = 0.02; r = 0.29) with calf ADG between d 30 and 60. These relationships suggest that average milk energy output on d 30 and/ or d 60 may be representative of milk energy consumption by calves from d 30 through 60. Thus, the lack of response for calf ADG between d 30 and 60 in the current study was not surprising considering there was no difference in 24-h milk energy output between d 30 and 60 of lactation.
In conclusion, prepartum management of cows to achieve BCS 4 at parturition resulted in a decrease in overall pregnancy rate. The provision of high-linoleate and high-oleate safflower seeds during early to peak lactation did not seem to influence nutrient partitioning in beef cows. Calf performance was not influenced by either BCS at parturition or maternal dietary treatment. Further research should be directed at investigating the effect of BCS at parturition on metabolic signals associated with lipid storage and mobilization to allow development of feeding strategies to improve the status of cows in suboptimal condition as the breeding season approaches.
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Footnotes |
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2 Correspondence: Department 3684, 1000 E. Univ. Ave. (phone: 307-766-5173; fax: 307-766-2355; e-mail: brethess{at}uwyo.edu).
Received for publication February 21, 2005. Accepted for publication August 18, 2005.
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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S. L. Lake, E. J. Scholljegerdes, W. T. Small, E. L. Belden, S. I. Paisley, D. C. Rule, and B. W. Hess Immune response and serum immunoglobulin G concentrations in beef calves suckling cows of differing body condition score at parturition and supplemented with high-linoleate or high-oleate safflower seeds J Anim Sci, April 1, 2006; 84(4): 997 - 1003. [Abstract] [Full Text] [PDF]
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S. L. Lake, E. J. Scholljegerdes, D. M. Hallford, G. E. Moss, D. C. Rule, and B. W. Hess Effects of body condition score at parturition and postpartum supplemental fat on metabolite and hormone concentrations of beef cows and their suckling calves J Anim Sci, April 1, 2006; 84(4): 1038 - 1047. [Abstract] [Full Text] [PDF]
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S. L. Lake, E. J. Scholljegerdes, V. Nayigihugu, C. M. Murrieta, R. L. Atkinson, D. C. Rule, T. J. Robinson, and B. W. Hess Effects of body condition score at parturition and postpartum supplemental fat on adipose tissue lipogenic activity of lactating beef cows J Anim Sci, February 1, 2006; 84(2): 397 - 404. [Abstract] [Full Text] [PDF]
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for control (P = 0.09), 2.18 to +