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Our hypothesis was that maternal nutrient restriction would negatively impact the endocrine and metabolic status of the pregnant cow, therefore influencing the mammary gland in preparation for lactation. We further hypothesized that earlier timing of realimentation could prevent negative impacts of nutrient restriction. The objectives were to investigate the influence of nutrient restriction and realimentation during early to late gestation on endocrine profile, umbilical hemodynamics, and mammary gland development and hemodynamics in pregnant beef cows. In Experiment 1, on d 30 of pregnancy cows (initial BW = 667.5 ± 13.4 kg, BCS = 6.2 ± 0.1) were randomly assigned to one of 3 treatments: 1) 100% NRC requirements from d 30 to 254 of gestation (CCC; n = 6); 2) 60% NRC from d 30 to 85, thereafter being re-alimented to 100% NRC to d 254 (RCC; n = 5); 3) or receive 60% NRC from d 30 to 140, thereafter being re-alimented to 100% NRC to d 254 (RRC; n = 6). Cows were returned to a common outdoor facility for calving thereafter and were fed ad libitum. In Experiment 2, on d 30 of pregnancy, cows (initial BW = 620.5 ± 11.3 kg, BCS = 5.1 ± 0.1) were randomly assigned to dietary treatments including: control (CON; 100% NRC; n = 18) and nutrient restriction (RES; 60% NRC; n = 30). On d 85 of pregnancy, cows were either slaughtered (CON, n = 6 and RES, n = 6), remained on control (CC; n = 12) and restricted (RR; n = 12) treatments, or were realimented to control (RC; n = 11). On d 140 of pregnancy, cows were either slaughtered (CC, n = 6; RR, n = 6; RC, n = 5), remained on control (CCC, n = 6; RCC, n = 5), or were realimented to control (RRC, n = 6). On d 254 of pregnancy, all remaining cows were slaughtered (CCC, n = 6; RCC, n = 5; RRC, n = 6). Mammary hemodynamics and endocrine profile were measured. Serum urea nitrogen, NEFA, as well as fetal parameters were measured in Experiment 1; whereas in Experiment 2, mammary gland development was recorded. In Experiment 1, RRC cows had lower dry matter intake (P = 0.001) and consequently lower BW change (P = 0.06). However, maternal nutrition did not alter mammary hemodynamics, hormonal patterns, and fetal characteristics (P 0.11). In Experiment 2, CCC cows had increased (P = 0.02) mammary gland blood flow ipsilateral to the gravid horn as well as greater (P = 0.02) mammary gland fat on d 254. Nevertheless, plane of nutrition did not alter hormonal concentrations nor mammary gland characteristics (P 0.15). These data indicate that nutrient restriction did not alter mammary hemodynamics nor endocrine profile throughout gestation. |
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