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ANIMAL PRODUCTION |
* University of Nebraska West Central Research & Extension Center, North Platte 69101; and
and
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: fertility • fetal programming • heifer development • maternal nutrition • protein supplement
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Jordon et al., 2002). Protein supplements are commonly fed during late gestation to maintain cow body condition. These supplements add expense and do not always improve subsequent reproductive performance of the cow herd, but the cost of supplementation is justified by increased weaning weights and a greater proportion of live calves at weaning (Stalker et al., 2006). Additionally, allowing cows to graze cool-season meadows during early lactation, when nutrient requirements are greatest (NRC, 2000), increases calf weaning weight and system profitability compared with feeding cool-season grass hay (Stalker et al., 2006).
Fetal programming is the concept that maternal stimuli during fetal development influence the physiology of the fetus and postnatal growth and health (Barker et al., 1993). There are only limited data concerning the influence of late-gestation nutrition of ruminants on reproductive performance of their female progeny. Primiparous heifers restricted to 65% of the NRC recommended energy intake during the final 100 d of pregnancy had calves with lighter birth weights and a reduced weaning percentage compared with heifers fed at NRC recommendations (NRC, 1970). Age at puberty of heifer calves from primiparous dams that were energy-restricted was increased by 19 d, but pregnancy rate of the heifer calves was not measured (Corah et al., 1975). Furthermore, energy restriction of ewes for 10 d during late gestation resulted in altered adrenal steroid production in adult female progeny (Bloomfield et al., 2003).
The objectives of the current study were to determine if feeding supplemental protein to cows during late gestation or allowing cows to graze subirrigated meadow during the postpartum period influences subsequent growth and reproductive performance of their heifer calves.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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During the last trimester of gestation, from December 1 through February 28, cows were divided into eight 32-ha upland pastures. Upland range sites at GSL are dominated by little bluestem [Andropogon scoparius (Michx.) Nash], prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.], sand bluestem (Andropogon hallii Hack.), sand lovegrass [Eragrostis trichoides (Nutt.) Wood], and blue grama [Bouteloua gracillis (H.K.B.) Lag. Ex Griffiths] (Adams et al., 1998). On a pasture basis, cows received the equivalent of 0.45 kg/d of a 42% CP supplement fed 3 times/wk or no protein supplement. The supplement contained 73.3% TDN and consisted of 50.0% sunflower meal, 47.9% cottonseed meal, and 2.1% urea on a DM basis. Cows were fed hay in a drylot as a single group during the calving season, March 1 to April 20 (average calving date, March 27).
From May 1 to 31, half of the cows remained in the drylot and were fed cool-season grass hay, and the other half grazed a common, 58-ha, subirrigated meadow pasture. The primary forage species on subirrigated meadow at GSL are smooth bromegrass (Bromus inermis Leyss.), redtop bent (Agrostis stolonifera L.), timothy (Phleum pratense L.), slender wheatgrass [Elymus trachycaulum (Link) Gould ex Shinn.], quackgrass [Elytrigia repens (L.) Nevski.], and Kentucky bluegrass (Poa pratensis L.; Adams et al., 1998). On June 1, cows were again combined and were managed in a common group on upland range throughout the breeding season and the remainder of the production cycle. Each year, cows were exposed to fertile bulls for 60 d. Additional supplement composition, diet quality, cow performance, and steer feedlot performance data were reported by Stalker et al. (2006).
Heifer Management
Treatments were applied only to the dam during late gestation or early lactation, and no further treatments were applied to their heifers. Data include records from 84 heifers born to unsupplemented cows and 86 heifers born to cows supplemented with protein for the last trimester of gestation. Furthermore, 87 of the heifers’ dams were fed hay in a drylot for the month of May, and 83 of the heifers’ dams grazed subirrigated meadow. During yr 1, heifers (n = 66) were managed until weaning as a single group at GSL, and data from yr 1 are limited to birth and weaning information. Weaning weights for all years were adjusted for calf age, but not for age of the dam because cows were stratified by age and assigned randomly to treatment when the experiment began.
Heifers from yr 2 (n = 46) remained at GSL, and reproduction and calving data were collected in addition to birth and weaning records. Heifers were weaned on 8 October and remained on upland range throughout development. From weaning until 20 May, heifers from yr 2 were supplemented as a group with 0.45 kg·heifer–1·d–1 of a 28% CP (DM basis) supplement in cake form. The supplement contained 62.0% dried distillers grains plus solubles, 10.6% wheat middlings, 9.0% cottonseed meal, 5.0% dried corn gluten feed, 3.0% molasses, 3.0% calcium carbonate, and 2.0% urea on a DM basis. Additionally, the supplement was formulated to meet vitamin and trace mineral requirements of the heifers and to supply 80 mg·heifer–1·d–1 of monensin (Rumensin, Elanco Animal Health, Indianapolis, IN). The proportion of heifers cycling before the beginning of the breeding season in yr 2 was determined by evaluating the progesterone concentration in 2 blood samples collected 10 d apart. Heifers from yr 2 were exposed to fertile bulls maintained at a ratio of approximately 1:25 (bulls:heifers) for a 45-d breeding season. Overall pregnancy rates were determined using transrectal ultrasonography at approximately 30 d after the end of the breeding season and were confirmed by calving date. Body condition score (Wagner et al., 1988) was also determined at pregnancy diagnosis. The percentage of heifers calving during the first 21 d of the calving season was calculated using the date on which the first heifer calved as the initial day of the calving season.
Birth, weaning, reproductive, and calving data were collected from heifers in yr 3. Heifers born in yr 3 (n = 58) were weaned on October 1, remained at GSL for 109 d after weaning, and were then transported 1,013 km to the North Dakota State University Animal Nutrition and Physiology Center, Fargo, ND to evaluate the efficiency of gain on an individual basis. Collection of individual intake and G:F was not feasible at GSL because of the facilities. After a 14-d adaptation and training period, heifers were individually fed for 84 d using Calan gates (American Calan, Northwood, NH). Heifers were exposed to 14 h of light and 10 h of dark each day.
The ration consisted of ad libitum consumption of cool-season grass hay (7.5% CP, 71% NDF, 52% ADF; DM basis) fed in the morning in sufficient quantity to insure that hay remained at the next feeding, and the heifers were supplemented daily with 0.90 kg of sun-flower meal-based pellets (34.6% CP, 35.02% NDF, 21.71% ADF, DM basis) that were fed each afternoon. The supplement was fed in the afternoon to prevent the heifers from forcing hay out of the bunks while attempting to select for the supplement. Orts were collected twice weekly and analyzed for DM to determine DMI.
Two-day, consecutive BW and BCS were taken at the beginning and end of the feeding period, with interim BW and blood samples collected every 14 d. After completion of the individual feeding period on May 17, 2005, heifers were transported 1,034 km to the West Central Research and Extension Center, North Platte, NE. Pre-breeding BW were collected 14 d later, and heifers were exposed to bulls (1:26, bulls:heifers) for a 45-d breeding season. Pregnancy diagnosis was performed via transrectal ultrasonography approximately 50 d after completion of the breeding season, and calving dates were also recorded.
Blood Collection and Assays
Blood samples were collected via coccygeal venipuncture, cooled immediately on ice, and serum was harvested via centrifugation at 1,349 x g and frozen at –20°C until analysis. Serum progesterone concentrations in yr 2 were determined by direct solid-phase RIA (Coat-A-Count, Diagnostics Products Corp., Los Angeles, CA) without extraction, as described by Melvin et al. (1999). Samples from yr 2 were evaluated in a single assay, with an intraassay CV of less than 10%. Samples from yr 2 were evaluated in a single assay, with an intraassay CV of less than 10%.
Serum progesterone concentrations in samples from yr 3 were analyzed by solid-phase, competitive, chemiluminescent enzyme immunoassay (Immulite 1000, Diagnostics Products Corp.). Within assay variability for progesterone was determined by assaying replicate samples from a pool of serum from cycling cows to which known quantities of progesterone had been added (0.0, 0.25, 1.0, 5.0, and 25.0 ng/mL). The resulting concentrations (mean ± SEM) after subtraction of the serum blank (0.51 ± 0.03 ng/mL; n = 4) averaged 0.29 ± 0.08 (n = 4), 1.26 ± 0.01 (n = 4), 6.42 ± 0.38 (n = 4), and 26.2 ± 0.42 (n = 4) ng/mL, respectively. Coefficients of variation averaged 8.0, 13.9, 1.1, 7.8, and 2.2% for the serum blank and the samples with 0.25, 1.0, 5.0, and 25.0 ng/mL of added progesterone, respectively. A correlation of the Immulite chemiluminescent enzyme immunoassay with the Coat-A-Count RIA using 37 samples resulted in a regression of Immulite = (0.51 x RIA) + 0.92 (r = 0.95). For the current study, inter- and intraassay CV for the Immulite (n = 2 assays) were 9.8 and 7.6%, respectively, and the recovery rate was greater than 90%. Wilson et al. (1998) compared the chemiluminescent and RIA procedures used in the current study in human serum and plasma and found similar results with both methods. A progesterone concentration greater than 1 ng/mL was interpreted to indicate ovarian luteal activity.
Statistical Analysis
The statistical model was appropriate for a 2 x 2 factorial arrangement of treatments in a switchback design. Performance data were analyzed using PROC MIXED (SAS Inst. Inc., Cary, NC). Reproductive and calving difficulty data were analyzed using 
2 procedures in PROC GENMOD of SAS. Individual heifer was considered the experimental unit, and the statistical model included dam treatment during late gestation and dam treatment during early lactation as fixed effects. The interaction between late gestation and early lactation treatments was included for data sets when significant and was removed from the final analysis if it was not significant. In multiyear analyses, year was included in the model as a random variable using the random statement. Pen was included in the random statement for heifers in the individual feeding experiment (yr 3).
Residual Feed Intake Calculation
For yr 3, residual feed intake (RFI) was calculated by simultaneously regressing DMI on midtest BW and ADG using PROC REG of SAS, as described by Cammack et al. (2005). The slope coefficients (bm and bg, respectively) from these analyses were then used to predict DMI using the following equation: Predicted DMI = average DMI of the group + [bm x (individual midtest BW – group average for midtest BW)] + [bg x (individual ADG – group average for ADG)]. Residual feed intake was calculated as the difference between observed and predicted DMI; therefore, lower values indicate greater efficiency.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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).
Heifer birth and growth data are summarized in Table 1. Dam nutrition did not affect (P > 0.10) heifer birth date or birth weight. These data agree with observations of Hough et al. (1990) who reported similar birth weights of calves born to mature cows restricted to 57% of NRC requirements for protein and energy or fed to meet nutritional requirements the last 90 d of gestation. Also in agreement with the current study, Carstens et al. (1987) fed isoenergetic diets with 91 or 55% of CP requirements to cows from 190 d of gestation until term without altering progeny birth weight. However, reduced birth weights were observed when pregnant nulliparous heifers fed approximately isonitrogenous diets were restricted to 65% of required energy intake for 100 d before calving, compared with their cohorts fed to meet energy requirements (Corah et al., 1975). Although fetal growth is maximized during the last trimester of gestation (Eley et al., 1978), maternal undernutrition during this time does not predictably reduce birth weight. Differences in protein and energy status of dams during late gestation did not influence heifer calf birth weight in the current study.
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). In contrast, weaning weight was not affected by nutrient restriction of cows during late gestation (Hough et al., 1990). However, energy restriction of pregnant nulliparous heifers resulted in reduced calf weight at weaning despite similar dam milk production (Corah et al., 1975), which was not measured in the current study. In the current study, heifers from cows grazing subirrigated meadows during early lactation had increased actual (P = 0.09) and adjusted (P = 0.07) weaning weight compared with heifers from cows fed hay, which agrees with previous reports indicating improved energy status of cows during early lactation increased progeny weaning weight (Houghton et al., 1990; Spitzer et al., 1995). In sheep, high levels of dam nutrition during the final 100 d of gestation and initial 100 d of lactation increased lamb weaning weights (Gunn et al., 1995), which agrees with data from protein supplemented and meadow grazing treatments reported in this study.
Prebreeding BW and BW at pregnancy diagnosis were greater (P < 0.04) for heifers from protein-supplemented dams than heifers from unsupplemented dams, but early lactation treatment did not affect (P > 0.50) either weight. Similar to the current study, 4 and 12 mo BW of progeny from ewes restricted 6 wk prepartum to 12 mo after birth (Gunn, 1977) were increased. In these studies (Gunn, 1977; Gunn et al., 1995), maternal nutrition treatments were determined by available pasture quality and supplemental feeding regimen. In contrast, energy restriction of ewes for 10 or 20 d during late gestation did not affect BW of female progeny at 30 mo of age (Oliver et al., 2002; Bloomfield et al., 2003), and restricting ewes to 50% of energy requirements beginning at d 110 of pregnancy did not alter yearling weight compared with offspring of ewes fed to meet energy requirements (Gardner et al., 2005). Average daily gain between weaning and beginning of the first breeding season for heifers from yr 2 and 3 of the current study was not affected (P = 0.32) by dam treatment. Heifers born to protein-supplemented cows gained 0.24 ± 0.01 kg/d compared with 0.23 ± 0.01 kg/d for heifers from unsupplemented dams. Therefore, weaning weight advantage of heifers from protein-supplemented cows was maintained through their second pregnancy diagnosis.
Data from the individual feeding experiment (yr 3) are presented as simple effects due to the interaction of dam nutrition during late gestation and early lactation (Table 2). Heifers from protein-supplemented cows were heavier (P = 0.08) at the end of the 84-d experiment but had similar initial BW (P = 0.19) and similar BCS at both time points (P > 0.20) compared with heifers from cows that were not supplemented. Dam nutrition during early lactation did not affect BW or BCS (P > 0.20) of heifer calves. Neither ADG nor G:F was affected (P > 0.25) by maternal nutrition.
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). Dry matter intake and RFI were affected (P < 0.09) by the interaction of maternal nutrition during late gestation and early lactation. Heifers born to protein-supplemented dams had greater DMI (P = 0.09) if their dams were fed hay during early lactation, but not if their dams grazed meadows in early lactation (P > 0.10). Similarly, heifers from protein-supplemented dams had greater RFI (P = 0.07) if their dams were fed hay during early lactation, but not if their dams grazed meadows during early lactation (P > 0.10). Greater RFI values indicate heifers from protein-supplemented cows fed hay during early lactation were less efficient than heifers from unsupplemented cows fed hay during early lactation. In this data set, it appears selecting for G:F based on RFI would result in reduced DMI, but not improved ADG, because there was not a correlation between RFI and ADG (P = 1.0). Previous experiments also indicate a lack of correlation between RFI and ADG (Arthur et al., 2001; Carstens et al., 2002). In fact, heifers with more favorable RFI also had numerically lower ADG, but differences were not statistically significant (P = 0.15). Causes for the interaction between protein supplementation during gestation and early lactation plane of nutrition on DMI and RFI are not easily explained and are not supported by feedlot ADG or G:F data from the steer mates to heifers used in the current study (Stalker et al., 2006). Gain to feed ratio was not affected by treatment (P > 0.25), in agreement with feedlot data from steer cohorts.
There was no effect (P > 0.15) of dam nutrition on the proportion of heifers from yr 2 and 3 exhibiting ovarian luteal activity before the breeding season, nor was there a difference in age at puberty of heifers born in yr 3 (P > 0.45; Table 3). This is in agreement with Corah et al. (1975) who also did not detect a difference in age at puberty in female progeny of primiparous heifers restricted to approximately 65% of NRC recommended energy intake for the final 100 d of gestation. The severity of restriction imposed by Corah et al. (1975), and the moderate negative energy balance experienced by mature cows used in this study indicate dam energy deficiency during late gestation is unlikely to influence attainment of puberty in heifer progeny.
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; P = 0.005). Overall pregnancy rate was 93 vs. 80% (P = 0.05) for heifers from protein-supplemented or unsupplemented dams, respectively. This is independent of age at puberty or estrous cyclicity immediately before the breeding season and suggests a fetal programming effect of late gestation dam nutrition on subsequent heifer fertility. In ruminant animals, ovarian folliculogenesis and endometrial gland development is completed late in gestation (Gray et al., 2001; Rhind et al., 2001). Therefore, these tissues may be involved in the programming of fertility observed in the current study.
First parity average calving date, calving difficulty, and calf birth weight were similar for heifers born to protein-supplemented and unsupplemented cows (P > 0.15; Table 3). Furthermore, there was no difference (P > 0.18) in pregnancy rates, calving date, calving difficulty, or calf birth weight during the initial calving season due to early lactation dam treatment. Weight before the second breeding season for heifers born in yr 2 and 3 was 446 ± 6 kg for heifers from protein-supplemented dams, compared with 422 ± 6 kg for heifers from unsupplemented dams (P = 0.005) but was unaffected by dam nutrition during early lactation (P = 0.10; data not shown). Weight records before second breeding include only females that became pregnant during the first breeding season, so more heifers from protein-supplemented cows are represented than daughters of unsupplemented cows. In a related study, Stalker et al. (2006) reported increased weaning and initial feedlot BW of steers born to protein-supplemented dams but similar final BW compared with steers from unsupplemented dams. Based on weight before the second breeding season, it appears greater postweaning BW of heifers from protein-supplemented cows are maintained through 3 yr of age. Protein supplementation of cows grazing dormant Sandhills range during late gestation resulted in heifer progeny with increased BW from weaning through 3 yr of age. Perhaps more importantly, heifers from protein-supplemented cows had greater pregnancy rates and were more likely to calve in the initial 21 d of their first calving season.
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Footnotes |
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2 Corresponding author: rfunston2{at}unl.edu
Received for publication May 23, 2006. Accepted for publication October 30, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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