Repeatability of Calving Difficulty
Recently an Oklahoma cow/calf producer asked about the repeatability of calving difficulty in young cows. He had a two-year-old heifer that endured a very difficult delivery. After the event is over and the cow and calf are doing well, the rancher can’t help but ask the question: “If a heifer has calving difficulty this year, what is the likelihood that she will have trouble again next year?” That question is followed by the thought of the money invested in this young heifer to grow her to a two-year old. Should she be culled next fall because of calving difficulty this spring?
A look back through the scientific literature sheds some light on this subject. Research conducted by Colorado State University and published in 1973 looked at parturition records of 2733 Hereford calves sired by 123 bulls and born to 778 cows/heifers. (Source: Brinks, et al. Journal of Animal Science 1973 Vol. 36 pp 11-17) .A repeatability estimate was obtained from heifers calving both as 2 year- and 3-year-olds. The estimate was 4.5%. Of 195 heifers which had no difficulty in calving at two years of age, 7.2% had difficulty as 3 year olds. Of the 77 two-year old heifers which experienced calving difficulty, 11.7% had difficulty again as 3-year-olds.
Heifers that experienced calving difficulty as 2 year-olds weaned 59% of calves born, whereas, those having no difficulty weaned 70% of calves born. Calving difficulty as 2 year-olds affected the number of calves weaned when 3 years of age and also the weaning weight of those calves. Heifers having calving difficulty as 2-year-olds weaned a 63% calf crop as 3-year-olds. Heifers having no difficulty as 2 years-olds weaned a 77% calf crop as three-year-olds.
From this research we learned that calving difficulty as a two-year-old had a profound effect on productivity. The likelihood that calving difficulty will happen again next year is only slightly greater than in heifer counterparts that calved unassisted this year. Proper heifer development to a body condition score of 5.5 or 6 at calving, along with breeding heifers to low birth weight EPD bulls should help reduce calving difficulty in two-year olds.
