Relationships between body condition score, milk yield, insulin-like growth factor-I concentration and resumption of ovarian activity in beef cows

A study was conducted to investigate the relationships between milk yield, body condition score (BCS), plasma concentrations of insulin-like growth factor (IGF-I) and the resumption of ovarian cyclicity in Sanga cows. Sixteen multiparous Sanga cows were grazed extensively on natural pasture. Cows were weighed monthly and scored for body condition weekly using a 9-point score (1= very thin and 9 = obese). Milk yield was determined daily. Blood samples were taken from cows once every week, from week 1 to 13 postpartum and processed for plasma. Resumption of postpartum ovarian cyclicity in cows was determined by measuring plasma progesterone concentrations from week 1 to 13 (90 days) postpartum. The cows were classified as having resumed ovarian cyclicity when progesterone concentration of .1.0 ng/mL was recorded in two consecutive weekly samples. Based on the resumption of ovarian activity, cows were classified as early cycling (. 45 days postpartum), late cycling (46-90 days postpartum) or non-cycling (no resumption by 90 days postpartum). The concentration of IGF-I was measured from week 1 to 10 in plasma samples. Results from the present study indicate that 37.5% of cows commenced ovarian cyclicity earlier, 31.25% commenced ovarian cyclicity later, while 31.25% failed to resume ovarian cyclicity within the period of study. BCS was significantly greater (P < 0.05) in early cycling (5.12) or late cycling (5.11) cows than non-cycling (4.69) cows. Milk yield was significantly (P < 0.05) higher in late cycling (1.09 } 0.01 L/day) or non-cycling (1.10 } 0.01 L/day) cows than in early cycling cows (1.02 } 0.01 L/day). Early cycling (23.2 } 1.26 ng/mL) or late cycling (19.5 } 1.38 ng/mL) cows had greater (P < 0.05) plasma concentrations of IGF-I than non-cycling cows (14.7 } 1.38 ng/mL). Cows had poor metabolic status. Higher plasma concentrations of IGF-I in the early postpartum period were associated with early resumption of ovarian cyclicity in cows.Key words: Body condition score, insulin-like growth factor-I, ovarian cyclicity, Sanga co