The aim of this study was to evaluate the effect of a negative energy balance during the first third of gestation on metabolic, endocrine, and pregnancy recognition parameters in 2 beef cattle breeds adapted to semiextensive conditions. Seventy-five lactating Parda de Montaña and 40 Pirenaica multiparous cows rearing calves were synchronized and timed artificial inseminated (TAI) on day 76 postpartum. Cows were assigned to one of 2 diets (CONTROL or SUBNUT; 100% or 65% of their requirements supplied) until day 82 of gestation. Pregnancy was diagnosed 37 d post-TAI using ultrasound. Blood samples were obtained to determine metabolic (glucose, NEFA, β-hydroxybutyrate, cholesterol, and urea) and endocrine (IGF-1) status throughout the first third of gestation and to determine the concentrations of progesterone and pregnancy-specific protein B (PSPB) in the peri-implantational period. Undernutrition affected both cow and calf performance. The CONTROL cows maintained BCS and BW, whereas SUBNUT cows had negative daily gains. The CONTROL lactating calves had higher BW gains than SUBNUT. These negative effects were more evident in the Pirenaica breed, which was more sensitive to undernutrition. The negative energy balance was reflected in the cows’ metabolic profiles, with higher NEFA values and lower IGF-1 concentrations in SUBNUT cows. However, undernutrition did not affect dam pregnancy/TAI or pregnancy recognition and maintenance, confirming that during periods of undernourishment pregnant dams prioritize the allocation of dietary energy toward reproductive functions. Progesterone concentration on day 21 post-TAI (with a 4.8 ng/mL cut-off value) and PSPB on day 26 post-TAI (with a 0.57 ng/mL cut-off value) were determined as the earliest indicators to accurately establish dam pregnancy status, regardless of breed or nutrition treatment. In summary, early undernutrition affected cow performance and metabolic profiles and impaired lactating calf growth, but did not affect progesterone or PSPB concentrations or the pregnancy/TAI rate in suckled cows.

这项研究的目的是评估妊娠的前三分之一过程中负能量平衡对2种适应半广泛条件的肉牛的代谢，内分泌和妊娠识别参数的影响。在产后第76天，对75头泌乳的蒙大拿州帕尔达（Parda deMontaña）和40头比雷牛（Pirenaica）产小牛进行同步，并定时进行人工授精（TAI）。母牛被指定为两种饮食之一（对照或亚坚果；提供其需求量的100％或65％），直到妊娠第82天。在TAI后37天使用超声诊断为妊娠。获得血液样本以确定代谢（葡萄糖，NEFA，β-羟基丁酸酯，胆固醇，和尿素）和内分泌（IGF-1）的状态贯穿整个妊娠的前三分之一，并确定着床前后围孕期孕酮和妊娠特异性蛋白B（PSPB）的浓度。营养不良影响母牛和小牛的生产。对照母牛维持BCS和BW，而SUBNUT母牛每日负增长。对照泌乳小牛的体重增加高于SUBNUT。这些负面影响在对营养不良更为敏感的倍耐力品种中更为明显。负能量平衡反映在母牛的代谢谱中，SUBNUT母牛的NEFA值较高，而IGF-1浓度较低。但是，营养不良并不会影响大坝的妊娠/ TAI或妊娠的识别和维持，证实在营养不足的时期，孕妇的水坝将饮食能量的分配优先用于生殖功能。确定TAI后第21天的孕酮浓度（临界值为4.8 ng / mL）和TAI后第26天的PSPB（临界值为0.57 ng / mL）是准确建立大坝的最早指标。妊娠状态，无论是何种品种或营养治疗。总而言之，早期营养不良会影响奶牛的生产性能和代谢状况，并损害泌乳小牛的生长，但不会影响孕酮或PSPB的浓度或乳牛的妊娠/ TAI率。不论品种或营养处理方法如何，均以57 ng / mL的临界值作为准确确定水坝妊娠状态的最早指标。总而言之，早期营养不良会影响奶牛的生产性能和代谢状况，并损害泌乳小牛的生长，但不会影响孕酮或PSPB的浓度或乳牛的妊娠/ TAI率。不论品种或营养处理方式如何，均以57 ng / mL的临界值作为准确确定水坝妊娠状态的最早指标。总而言之，早期营养不良会影响奶牛的生产性能和代谢状况，并损害泌乳小牛的生长，但不会影响孕酮或PSPB的浓度或乳牛的妊娠/ TAI率。