A negative energy balance during the peri-implantational period reduces dam IGF-1 but does not alter progesterone or pregnancy-specific protein B (PSPB) or fertility in suckled cows

Abstract 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 two beef cattle breeds adapted to semi-extensive conditions. Seventy-five lactating Parda de Montana and 40 Pirenaica multiparous cows rearing calves were synchronized and timed artificial inseminated (TAI) on day 76 postpartum. Cows were assigned to one of two diets (CONTROL or SUBNUT; 100% or 65% of their requirements supplied) until day 82 of gestation. Pregnancy was diagnosed 37 days post-TAI using ultrasound. Blood samples were obtained to determine metabolic (glucose, NEFA, β-hydroxybutyrate, cholesterol and urea) and endocrine status (IGF-1) 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 cow 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 towards reproductive functions. Progesterone concentration on day 21 post-TAI (with a 4.8 ng/mL cutoff value) and PSPB on day 26 post-TAI (with a 0.57 ng/mL cutoff 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.