Sensitivity of ovulation detection and effects of genetic merit and protein degradability on reproduction in dairy cows

Abstract

Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 SENSITIVITY OF OVULATION DETECTION AND EFFECTS OF GENETIC MERIT AND PROTEIN DEGRADABILITY ON REPRODUCTION IN DAIRY COWS C. WESTWOODA, I. LEANA, J. GARVINA, N. WILLIAMSONB, J. DELLA VEDOVAA and R. KELLAWAY *Dept of Animal Science, University of Sydney, Camden, N.S.W. 2570 * Dept of Veterinary Clinical Sciences, Massey University, Palmerston North, New Zealand A While the addition of dietary undegraded (UDP) protein to dairy cow rations can increase milk yields, higher milk production is associated with reproductive failure (Lean et al. 1989). This study investigated the effect of rations that were isonitrogenous and isoenergetic, but differing in proportions of UDP relative to rumen degraded protein (RDP), UDP:RDP ratio (45:55 vs 15:85), on the sensitivity of detection of ovulation and oestrus, days to first ovulation and first oestrus. Eighty multiparous Holstein cows were randomised to 4 groups; low genetic merit (low Australian Breeding Value, ABV), low UDP; low ABV, high UDP; high ABV, low UDP; and high ABV, high UDP. Cows were individually -fed total mixed rations ad lib for 150 days of lactation. Days to first ovulation were assessed using milk for progesterone assay every third day from day 7 after calving. Oestrus was monitored by observation (approximately 14 hours per day), and use of KAMAR heatmount detectors (KAMAR Inc., Colorado, U.S.A.). Heats were recorded as standing, secondary signs (physical and behavioural) or a combination of these signs. Comparison of heat data with milk progesterone profiles of each cow indicated sensitivity of ovulation detection. Ovulation was defined by a milk progesterone concentration of less than 6 nmol/L within 1.5 days of observed oestrus followed by a luteal phase (progesterone greater than 6 nmol/L on 2 consecutive samples). For the purposes of investigating sensitivity of oestrus detection, all groups were combined. Table 1 shows that the specificity of detection of ovulation was best with KAMAR combined with standing heat (99%), satisfactory with a KAMAR heat with secondary signs (91%) and poor with KAMAR only heats (38 %). Errors in heat detection reduce insemination rates or increase non-oestrus inseminations, reduce conception rates, and increase calving intervals. Careful consideration is required before mating cows on KAMAR-only heats. Table 1. Sensitivity of visual indicators of ovulation . Table 2. Effect of protein degradability and genetic merit on days to first ovulation and oestrus 408