163 Growth trends in Bos grunniens raised in pasture-based systems in Eastern Kentucky

Bos grunniens (yak) are well-adapted to the rugged, high-altitude regions of central Asia where they are utilized for a variety of purposes. While the species is well-researched in its native land, limited research has been conducted in North America. The objective of this on-farm project was to evaluate performance of male and female growing yaks in pasture-based systems over two years. Grazing periods were 138 and 151 d for Yr 1 and Yr 2, respectively. The same plots were grazed both years, and pasture areas were approximately 0.49 ha each with three animals grazing each pasture in Yr 1 and two animals grazing each pasture in Yr 2. Pastures were comprised mostly of cool-season grasses with intermittent legumes and weeds. Yaks were assigned to one of four pastures based on sex with a total of six males (beginning weight 132.8 ± 13.5 kg) and six females (beginning weight 124.3 ± 34.4 kg) being grazed in Yr 1, and four males (beginning weight 157.3 ± 15.0 kg) and four females (beginning weight 160.9 ± 26.4 kg) being grazed in Yr 2. Animals in Yr 1 averaged 432 d of age, and animals in Yr 2 averaged 710 d of age at the start of the respective grazing periods. Pasture samples were collected throughout the study to assess nutritive value; botanical composition, presence of endophyte and concentration of ergovaline were also assessed. Tall fescue (Festuca arundinacea) samples collected at the end of the grazing period in Yr 2 averaged 32.65% infection and 146 ppb ergovaline. Data were analyzed using proc mixed procedure of SAS with sex and year as main effects and pasture as a random effect where α = 0.05. In Yr 1, males gained at a greater rate than females (0.45 kg/d vs. 0.23 kg/d; P = 0.0026). In Yr 2, a similar difference was observed for seasonal gains with males gaining 0.61 kg/d and females gaining 0.25 kg/d (P = 0.0003). A difference was also observed between growth rates of males in Yr 1 compared with males in Yr 2 (0.45 kg/d vs. 0.61 kg/d; P = 0.0024), but this difference was not observed in females. Gender can impact body weight gain in Bos grunniens raised in pasture-based systems with males gaining more rapidly than females.