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Effects of body condition score at parturition and postpartum protein supplementation on estrous behavior and size of the dominant follicle in beef cows^1,2

Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater 74078

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The objective of this study was to determine the effects of BCS at calving and the amount of postpartum protein supplementation on the dominant follicle (DF) and behavioral characteristics at the first postpartum estrus of mature beef cows. Multiparous Angus x Hereford cows (n = 45) were fed to calve in thin (T; < 5) or moderate (M; 5) BCS. Cows were stratified by BCS and calving date, and randomly assigned to receive lesser (L; 1.2 kg/d) or greater (G; 2.5 kg/d) amounts of a 42% CP supplement. All cows grazed the same native grass pasture and were fed in individual stalls for 49 ± 2 d. Beginning 20 d after calving, blood samples were collected from each cow thrice weekly, and estrous behavior was monitored continuously with a radiotelemetry system. At 4 to 16 h after the onset of estrus, size of the DF was determined by ultrasonography. Body condition score of T cows was less (P < 0.01) at calving than M cows; L and G cows had similar BCS at calving and at the end of the feeding period. Body weight gains during treatment did not differ for L or G cows. Duration from calving to first estrus was greater (P < 0.01) for T than M cows. The incidence of a short luteal phase before first estrus was not influenced by BCS or protein supplement. Concentrations of IGF-I in plasma tended (P < 0.07) to be greater and size of the DF was greater (P < 0.01) for M than T cows. Size of the DF tended (P < 0.06) to be greater for G than L cows. Duration and number of mounts received at the first estrus were not influenced by BCS or supplement. Pregnancy rate of M cows during the breeding season was greater (P < 0.05) than T cows. Postpartum protein intake and BCS at calving influenced the size of the DF at the first postpartum estrus in mature suckled beef cows. Cows should be managed to calve in moderate BCS and maintain BW after parturition to decrease the interval to first estrus, increase follicular development, and maximize pregnancy rate.

Key Words: beef cow • body condition • estrus • follicle • postpartum • protein

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Duration of the postpartum anestrous interval (PPI) is often a limiting factor to achieve optimal reproductive performance of beef cows. Duration of the PPI can be regulated by nutrient intake and body energy reserves (Dunn and Kaltenbach, 1980; Randel, 1990). Increasing nutrient intake before and after calving decreases the interval to first estrus and increases pregnancy rates (Wiltbank et al., 1962; Richards et al., 1986; Selk et al., 1988). When nutrient intake is limited, BCS of cows is decreased and percentage of cows detected in estrus during the breeding season is reduced (Richards et al., 1986; Spitzer et al., 1995). The relationship between BCS and postpartum nutrition on size of the dominant follicle at the first postpartum estrus is not established.

On the southern Great Plains, cows often graze native grass pasture that is not of sufficient quality to meet nutritional requirements during the early postpartum period (Johnson et al., 1998; Lents et al., 2000). Thus, supplemental protein is required to maintain BW and BCS of cows (McCollum and Horn, 1990; Lents et al., 2000) and can reduce the PPI (Sasser et al., 1988; Marston et al., 1995)

Secretion of LH and follicular growth can be enhanced by increasing postpartum nutrient intake (Perry et al., 1991; Grimard et al., 1995), and these effects may be dependent upon the BCS of cows. Metabolic hormones could mediate the effects of protein intake on reproductive function (Wettemann and Bossis, 2000; Diskin et al., 2003). Roles of plasma concentrations of IGF-I on regulation of ovulation of beef cows are not established (Stagg et al., 1998; Ciccioli et al., 2003; Wettemann et al., 2003). Therefore, the objective of this study was to determine the effects of BCS at calving and the amount of postpartum protein supplementation on ovarian function and behavioral characteristics at the first postpartum estrus of mature beef cows.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
All experimental procedures described were approved by the Oklahoma State University Animal Care and Use Committee.

Animals, Diets, and Treatments

Spring calving, multiparous Angus x Hereford cows (n = 45; BW = 478 ± 17 kg; age = 6.6 ± 0.5 yr) were used. Cows grazed native tallgrass prairie at the Range Cow Research Center near Stillwater. Predominant forage species were little bluestem (Andropogon scoparius) and big bluestem (Andropogon gerardii). Cows were fed 0.7 or 1.4 kg/d of a 42% CP supplement (soybean meal with 3% molasses and 2% dicalcium phosphate) beginning 115 d prepartum so that they would calve with a BCS (1 = emaciated and 9 = obese; Wagner et al., 1988) of thin (T; BCS <5) or moderate (M; BCS 5). At parturition (March 22 ± 3 d) T and M cows were stratified by calving date and randomly assigned to receive lesser (L; 1.2 kg/d) or greater (G; 2.5 kg/d) amounts of a 42% CP supplement. Supplement amounts were prorated for 6 d/wk of individual feeding in covered stalls. Cows were individually fed supplement until 60 d after parturition or until May 15 (supplementation averaged 49 ± 2 d). End of postpartum supplementation coincided with the time when adequate high-quality forage was available. During and after postpartum supplementation, all cows grazed the same native grass pasture. Body weight and BCS were determined monthly from 60 d prepartum until 210 d postpartum, after cows were denied access to feed and water for 16 h.

Blood Sampling and Hormone Assays

Blood samples were collected from each cow via coccygeal venipuncture 3 times weekly commencing at 20 d after calving until 21 d after the first estrus or until 130 d after calving if estrus did not occur. Blood (10 mL) was collected into tubes containing EDTA and placed on ice. Plasma was obtained by centrifugation (2,000 x g for 20 min at 4°C) and stored a –20°C until analyzed for hormone concentrations by RIA. Concentrations of progesterone in plasma were quantified with solid phase RIA validated for use in cattle (Vizcarra et al., 1997). Intra- and interassay CV were 4 and 7%, respectively. Concentrations of IGF-I in plasma were determined by RIA with acid-ethanol extraction (Echternkamp et al., 1990). Recombinant human IGF-I (R&D Systems, Minneapolis, MN) was used for standards. Intra- and interassay CV were 12 and 15%, respectively. A blood sample was collected, as described above, at 4 to 14 h after the onset of the first postpartum estrus. Plasma was obtained and concentrations of estradiol 17-β were determined by RIA (Vizcarra et al., 1997). The intraassay CV was 11% for the single assay in which all samples were quantified.

Estrous Behavior, Follicle Measurement, and Reproductive Performance

Beginning 20 d after calving, estrous behavior was monitored continuously with a radiotelemetry system (HeatWatch, DDx Inc., Denver, CO). Date, time, and duration of each mount received were used to determine duration of estrus and total number of mounts received during estrus for each cow. Onset of estrus was defined as the first of 2 mounts received within a 4-h period. End of estrus was defined as the last mount received that occurred at least 4 h before no further mounts were recorded during the next 12 h (White et al., 2002). Duration of luteal phases before and after estrus was determined by concentrations of progesterone. Duration of the luteal phase was characterized as short if a cow had plasma progesterone 0.5 ng/mL for <10 d, or normal if plasma progesterone was 0.5 ng/mL for 10 d (Ciccioli et al., 2003). Size of the preovulatory dominant follicle (DF) was determined at 4 to 16 h after the onset of the first postpartum estrus by transrectal ultrasonography (7.5-MHz probe, Corometrics Medical Systems, Wallingford, CT). Size of the DF was calculated as the mean of the longest and shortest diameter (Pierson and Ginther, 1988; Ciccioli et al., 2003; White et al., 2007). At 16 to 20 h after the onset of estrus, and at least 2 h after ultrasonography, cows were AI to a single bull by a trained technician. A 75-d natural service breeding season began 10 d after AI and continued until at least 120 d after calving. Overall pregnancy rate was determined by palpation per rectum at approximately 75 d after the end of the breeding season. Pregnancy rate to AI at the first estrus was determined from breeding date and subsequent calving date. Ovulation after first estrus was confirmed by at least 2 consecutive plasma samples with concentrations of progesterone 0.5 ng/mL (Wettemann et al., 1972). Duration of the PPI was determined as the number of days from parturition to first estrus with a subsequent normal luteal phase.

Statistical Analyses

Changes in BW, BCS, and PPI were analyzed as a completely randomized design with a 2 x 2 factorial arrangement of 4 treatments using a mixed model (PROC MIXED; SAS Inst. Inc., Cary, NC). The model included BCS at calving (T or M), postpartum supplement (L or G), and the interaction. Because cows were assigned to supplement treatment at calving and supplementation was terminated for all cows on the same day, calving date was included in the model as a covariate.

To be included in analyses for number of mounts received, duration of estrus, and size of the DF, cows had to exhibit an estrus followed by ovulation. Five cows failed to exhibit estrus or luteal activity during the experiment. Three cows exhibited estrus but did not have subsequent luteal activity, and were not included in the analyses. Complete estrous data for 3 cows were not available due to an electrical power outage on 2 separate days and data were not included in analyses because of uncertainty as to the onset of estrus. Thus, data from 9 LT, 9 GT, 6 LM, and 10 GM cows were used in these analyses. Number of mounts received, duration of estrus, and size of the DF were analyzed as a completely randomized design with a 2 x 2 factorial arrangement of 4 treatments using the model described above. The effect of treatments on concentrations of estradiol in plasma at first estrus was determined with the same model, with calving date and the number of hours after the initiation of estrus when the sample was collected included as covariates. Fisher’s-LSD was used to make preplanned comparisons between means when a significant (P < 0.05) F-test occurred. Effects of BCS at calving and postpartum protein supplementation on concentration of IGF-I before and after the end of supplementation, as well as before the first estrus, were determined by least squares analyses of variance using a mixed model with repeated measures over the same experimental unit using the MIXED procedure of SAS. All samples for 2 or 3 cows per treatment were included in an assay, and samples were distributed randomly within assay. The model included assay as a random effect; BCS at calving, postpartum protein supplementation, week postpartum, and all first- and second-order interactions were fixed effects. Cow within BCS x supplement treatment was the error term to test treatment effects (BCS, supplement, and the interactions), whereas the pooled residual was the error term to test week effect and all interactions with week. Degrees of freedom for the pooled error term were calculated using Satterthwaite approximation. A first-order autoregressive function with lag equal to 1 was used to model the covariance structure for the repeated measures. If interactions with week were significant, polynomial response curves of appropriate order were fitted and tested for heterogeneity of regression (Snedecor and Cochran, 1968) to evaluate BCS and supplementation effects. Chi-square analyses were used to determine the effects of postpartum supplementation and BCS on percentage of cows exhibiting estrus and AI pregnancy rate.

	RESULTS

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The 2 different amounts of prepartum protein supplementation resulted in greater (P < 0.01) BCS at calving for M than T cows (Table 1). Body condition score at calving did not differ (P = 0.15) between cows assigned to the L and G supplements after calving. Postpartum supplement intake did not affect (P = 0.24) change in BCS during the supplementation period. Body condition score of M cows was greater (P < 0.01) at the end of the feeding period than T cows (Table 1). Average BW before calving did not differ (P = 0.37) among cows assigned to L and G supplements, and BW change of cows during the supplementation period was not influenced by BCS at calving (P = 0.56) or supplement (P = 0.21; Table 1)

View larger version (19K): [in this window] [in a new window]   Figure 1. Least squares mean concentrations of IGF-I in plasma during 3 wk before and 3 wk after nutritional supplementation of postpartum cows with thin or moderate BCS at calving. Averaged across weeks, moderate cows tended (P = 0.07) to have greater concentrations of IGF-I than thin cows.

View larger version (12K): [in this window] [in a new window]   Figure 2. Least squares means (symbols) and least squares regression (line) for plasma concentrations of IGF-I before the first postpartum estrus. Concentrations of IGF-I increased (P = 0.03) linearly during 3 wk before the first estrus (0 wk).

Neither duration of the first estrus nor the number of mounts received at the first estrus was influenced by BCS at calving (P = 0.92 and P = 0.27, respectively) or amount of supplement (P = 0.99; P = 0.98, respectively; Table 2). Mean duration of the first postpartum estrus was 5.7 ± 0.8 h, and cows received an average of 11.9 ± 2.1 mounts. Size of the DF at the first estrus was larger (P < 0.01) for M cows than for T cows. The G cows tended (P < 0.06) to have a larger DF than L cows. Concentrations of estradiol in plasma were not influenced (P = 0.21) by time when blood samples were taken (10.2 ± 0.8 h) after the onset of estrus. Averaged over time, concentrations of estradiol in plasma at 4 to 16 h after the onset of the first postpartum estrus were 2.6 ± 0.3 pg/mL and were not affected by BCS at calving (P = 0.82) or supplement (P = 0.58; Table 2).

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Increasing protein intake for 49 d after parturition did not affect BCS and BW of mature lactating beef cows that calved in a BCS of 4 to 5 and grazed dormant native range. Providing additional supplemental feed to postpartum beef cows is associated with greater milk production (Perry et al., 1991; Marston et al., 1995; Lents et al., 2000). Cows fed the G supplement may have utilized additional feed to increase milk production rather than maternal tissue stores.

Amount of nutrient intake is directly related to concentrations of IGF-I in plasma of heifers (Armstrong et al., 1993; Yelich et al., 1996; Armstrong et al., 2001), as well as primiparous (Lalman et al., 2000; Ciccioli et al., 2003) and mature beef cows (Richards et al., 1991). Amount of protein supplementation did not alter plasma concentrations of IGF-I during or after the feeding period. Similarly, Spicer et al. (1991) found that plasma concentrations of IGF-I were not influenced by amount of intake when protein was adequate, which was the case in the current experiment. In addition, the end of supplemental feeding coincided with the availability of high-quality forage. This may have allowed cows to maintain a positive protein and energy balance that could have offset the potential decrease in IGF-I that would be expected when protein supplementation was terminated.

Feeding increased amounts of protein after parturition can decrease weight loss and reduce the interval from calving to first estrus (Rakestraw et al., 1986; Sasser et al., 1988). In contrast, duration of the PPI was not different for L and G cows. Lack of an effect of supplement is most likely attributable to the fact that L cows were able to maintain BW and BCS. In contrast, M cows returned to estrus approximately 30 d earlier than T cows, and M cows had a tendency to have greater concentrations of IGF-I in plasma during and after the supplement period compared with T cows. This is consistent with previous reports that body energy reserves at calving influence the interval to estrus and ovulation (Richards et al., 1986; Bishop et al., 1994; DeRouen et al., 1994). Reduced concentrations of IGF-I in plasma are associated with longer intervals to estrus and ovulation (Rutter et al., 1989; Beam and Butler, 1997; Roberts et al., 1997). Roberts et al. (1997) found that systemic concentrations of IGF-I were greater at 2 and 10 wk after parturition in cows that resumed estrous cycles by 20 wk compared with cows that were anestrus at 20 wk after calving. We determined that plasma concentrations of IGF-I increased linearly during the 4 wk before the first estrus. Stagg et al. (1998) monitored cows that were either suckled ad libitum or suckled once daily and observed a linear increase in IGF-I over a 75-d period after calving. The somewhat greater initial concentrations of IGF-I in M cows could have reduced, directly or indirectly, the duration of the PPI

First postpartum ovulation in beef cows is typically not accompanied by estrous behavior and is followed by a luteal phase of a shorter duration than normal (Murphy et al., 1990; Perry et al., 1991; Werth et al., 1996). Neither BCS nor amount of postpartum protein supplement influenced incidence of short luteal activity before or after the first estrus of mature suckled beef cows. This extends our observation in primiparous cows (Ciccioli et al., 2003) and substantiates that the duration of the estrous cycle after the first postpartum estrus usually is of normal duration and is not influenced by BCS or BW gain (Corah et al., 1974; Odde et al., 1980; Looper et al., 2003)

Feeding increased amounts of energy after parturition increased size of the DF in primiparous (Ciccioli et al., 2003) and mature (Grimard et al., 1995) beef cows. We report for the first time that increasing the amount of protein supplement fed to mature suckled beef cows grazing dormant forage after parturition tended to increase size of the DF independent of treatment effects on BW or BCS. Of particular interest, however, is the observation that cows that calved in moderate BCS had a larger DF at the first postpartum estrus than cows that calved in thin BCS. This was independent of nutrient intake after calving. A positive effect of greater BCS on follicles was recently reported in Brahman-influenced cows following synchronization of estrus (Flores et al., 2008). Larger follicles in M cows may have been due to somewhat greater concentrations of IGF-I in plasma before and after the feeding period. Greater nutrient intake after calving resulted in greater concentrations of insulin in plasma that were associated with larger DF (Ciccioli et al., 2003). Reduced nutrient intake of heifers results in more rapid turnover of DF, and the increased rate of turnover decreases DF size (Murphy et al., 1991). Cows that ovulate may have greater concentrations of IGF-I in blood than anovulatory cows (Beam and Butler, 1997), and plasma concentrations of IGF-I were increased before resumption of ovulation in nutritionally induced anovulatory heifers during realimentation (Bossis et al., 2000). Increased IGF-I may act on the hypothalamo-pituitary-ovarian axis to enhance secretion of gonadotropins and ovarian cell proliferation and steroidogenesis (Diskin et al., 2003).

Despite the fact that protein supplementation and BCS altered size of the DF at the first postpartum estrus, concentrations of estradiol in plasma were not different between treatments. This is consistent with our previous observation in which nutritional restriction of beef heifers reduced the size of the DF by 34% before concentrations of estradiol in plasma were decreased (Bossis et al., 1999). The lack of an effect of protein supplementation or BCS on concentrations of estradiol in the current experiment may be due to the fact that plasma samples were not collected from all cows at the same time after the start of estrus. Estradiol concentrations in blood are maximal shortly before or at the initiation of estrus (Henricks et al., 1971; Shemesh et al., 1972; Wettemann et al., 1972) and begin to decrease after the onset of estrus (Henricks et al., 1971; Chenault et al., 1975; Glencross et al., 1981). Previously we determined that concentrations of estradiol in plasma of beef cows did not begin to decrease until 8 h after the onset of estrus and were not significantly different until 16 h after onset (White et al., 2002). In the current study, time after the onset of estrus that blood samples were collected averaged 10 h, and estradiol concentrations were similar to maximal concentrations of estradiol we have previously reported (White et al., 2002). Additionally, in this experiment, concentrations of estradiol were not different between samples taken at 4 to 8 h, 8 to 12 h, or greater than 12 h after the start of estrus

Neither BCS nor supplement affected the percentage of cows that became pregnant after AI at the first estrus. Body condition score at calving is one of the most important factors influencing pregnancy rate (Wright et al., 1987; Selk et al., 1988), and M cows had greater pregnancy rates over the entire breeding period than T cows

When cows calve in thin BCS and are fed inadequate nutrients, fewer exhibit estrus (Richards et al., 1986; DeRouen et al., 1994; Spitzer et al., 1995). Neither BCS nor postpartum protein supplementation influenced characteristics of estrous behavior at the first postpartum estrus. This result is similar to our observation in primiparous beef cows (Ciccioli et al., 2003) but differs somewhat from those in Brahman-influenced cows (Flores et al., 2007). Differences in breed type (Hereford x Angus versus Brahman-influenced) and the type of estrus evaluated (spontaneous vs. synchronized) may influence estrous behavior. In addition, the minimal but significant difference in BCS of the T and M cows may not have been great enough to detect a significant effect on estrous behavior

Average duration of estrus (5.7 h) and number of mounts received (11.8) for mature cows in the current experiment were similar (5.6 h and 16.8 mounts) to those at the first postpartum estrus of primiparous cows (Ciccioli et al., 2003) and were less than for nonlactating beef cows (15.7 h and 46.7 mounts; White et al., 2002). Cow age, season, environment, management, and lactation could influence estrous behavior. Primiparous dairy cows were in estrus for almost 50% less time than multiparous cows (Walker et al., 1996). Mature beef cows were estrus longer and received fewer mounts in summer than during winter or spring (White et al., 2002). Duration of estrus and the number of mounts received were increased when more cows are estrus (Hurnik et al., 1975; Flores et al., 2006). First postpartum estrus of each cow occurred at random throughout the experiment. Thus, only a single cow was observed to be in estrus at any given time. Although cows were managed together at all times, the minimal number of cows in estrus may account for differences between studies

Protein supplementation and BCS influenced development of the DF at the first postpartum estrus. Cows in thin BCS maintained BW and BCS with postpartum protein supplementation but had a longer PPI. Circulating concentrations of IGF-I tended to be increased in cows with greater BCS at calving and were increased in all cows before the first postpartum estrus. With less than a 6 h duration of estrus, visual observation should be increased and estrous detection aids should be used to help identify the first postpartum estrus of beef cows. Cows should be managed to calve in moderate BCS and to maintain BW after parturition to decrease the interval to first estrus, increase follicular development, and maximize fertility.

	Footnotes

 
¹ Approved by the director of the Oklahoma Agric. Exp. Sta. This research was supported under project H-2331.

² Human IGF-I antiserum was obtained from A. F. Parlow, National Hormone and Pituitary Program, Harbor-University of California, Los Angeles, Medical Center.

³ Present address: Animal and Dairy Science Dept., The University of Georgia, Athens, GA 30602.

⁴ Present address: Dept. of Agriculture, Cameron University, Lawton, OK 73505.

⁵ Deceased.

⁶ Corresponding author: bob.wettemann{at}okstate.edu

Received for publication April 20, 2008. Accepted for publication May 21, 2008.

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Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 


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