Effects of feeding stockpiled tall fescue versus summer-baled tall fescue-based hay to late gestation beef cows: I. Cow performance, maternal metabolic status, and fetal growth

[摘要] We hypothesized that cows grazing stockpiled tall fescue (STF) during late gestation would have increased nutrient intake, resulting in improved metabolic status and fetal growth compared with cows consuming summer-baled tall fescue hay. Multiparous, spring-calving, crossbred beef cows (year 1: n = 48, year 2: n = 56) were allocated by body weight (BW), body condition score (BCS), age, service sire, and expected calving date to 1 of 2 forage systems (4 rep/system) in mid-November on day 188 of gestation: strip-graze endophyte-infected STF in 4.05 ha pastures or consume ad libitum endophyte-infected summer-baled tall fescue-based hay in uncovered dry lots. Treatments were terminated 1 wk postpartum, and cow-calf pairs were managed together until weaning. Data were analyzed with forage system, year, and their interaction as fixed effects. Sampling day was a repeated effect for cow metabolites and hormones. Calf date of birth was in the model when P < 0.25; pasture or pen was the experimental unit. Cow prepartum BW was not affected (P ≥ 0.424) by forage system, but cows grazing STF tended (P = 0.09) to have greater BCS at day 35 and had greater (P = 0.03) final precalving BCS than hay-fed cows. Additionally, final precalving 12th rib fat thickness tended (P = 0.09) to be greater for STF than hay-fed cows. Calves born to cows fed hay only weighed 10.2% less (P = 0.03) at birth than calves born to cows consuming STF, indicating reduced fetal growth. Postpartum cow BW, BCS, first service conception rate, and overall pregnancy rate were not affected (P ≥ 0.15) by late gestational forage system. After day 0, serum urea N was greater (P < 0.001) in cows consuming STF on all days measured. Cows grazing STF also tended (P = 0.08) to have greater plasma glucose than cows consuming hay. Serum nonesterified fatty acids (NEFA) were greater (P < 0.001) in cows grazing STF on day 56 in year 1 and on day 77 and 99 in year 2. Serum triiodothyronine was less (P = 0.03) on day 0, but greater (P = 0.004) on day 99, in cows grazing STF. Cows grazing STF tended (P = 0.06) to have greater thyroxine on day 77 in year 1. Serum cortisol was greater (P = 0.003) on day 35 and tended (P = 0.10) to be greater on day 99 in cows grazing STF. Calf birth weight was positively correlated with prepartum maternal serum urea N (r = 0.31, P = 0.002) and NEFA (r = 0.12, P = 0.005). In this study, cows grazing STF had increased nutrient intake during late gestation, resulting in greater fetal growth.

[学科分类] 动物科学