Sex and environment-biased maternal investment in cattle

Mothers must allocate limited resources between raising their offspring and maintaining their own biological functions. In both wild and livestock populations, food availability (forage) can fluctuate based on climate, soil fertility, and annual rainfall. As a result, mothers and their offspring must adapt to these challenges, particularly when environmental quality declines. In this study, we investigated whether maternal investment is influenced by the sex of the progeny and environmental conditions, using coefficients of variation for each trait as a measure of evolvability. We focused on three pre-weaning growth traits in cattle: birth weight (BW), body weight at 120 days (BW120), and at 210 days (BW210). Environmental conditions were categorized as low or high quality, depending on whether the calves came from a management group (cohort) with a phenotypic mean below or above the overall trait mean, respectively. The additive genetic coefficients of variation for body weights were consistently higher in females than in males (BW: 6.74 vs. 5.98; BW120: 6.21 vs. 5.38; BW210: 6.07 vs. 4.90). In contrast, the coefficients for maternal effects were lower in females than in males across all traits: BW (3.21 vs. 3.92), BW120 (5.52 vs. 6.09), and BW210 (5.30 vs. 5.64). However, these differences were not significant for BW210, likely due to calves beginning to reduce their exclusive milk intake at this point, thereby decreasing maternal investment. These findings suggest that, under limited environmental resources, maternal investment in cattle is sex-biased until 120 days of age, with cows increasing their investment to wean stronger calves.