Abstract

Positive relationships between concentrations of progesterone in milk and subsequent pregnancy rates suggest that measurement of milk progesterone concentration at selected times following insemination may facilitate identification of cows for strategic progesterone supplementation to enhance the probability of pregnancy. This study investigated some factors associated with variation in milk progesterone concentration. Following a standard oestrus synchronisation treatment with CIDR-BTM devices (InterAg, NZ), cloprostenol (Estroplan injection, Parnell Laboratories NZ Ltd, NZ) and oestradiol benzoate (CIDIROL Injection, InterAg, NZ) every cow artificially inseminated (AI) at 72 h after CIDR-BTM withdrawal (Day 0) was enrolled in the trial. Milk samples (fore-milk: Herd 1, n = 153, Holstein-Friesian; HF; composite: Herd 2, n = 50 HF and 76 Jersey; J) were taken 4, 8 and 22 days after AI to measure milk progesterone concentration. Pregnancy to the insemination was confirmed by rectal palpation 60-70 days later. Lower milk progesterone concentrations were found in fore-milk (Herd 1) than composite samples (Herd 2), but followed a similar pattern of change throughout Days 4, 8 and 22. Neither return to service, nor pregnancy status was associated with altered milk progesterone concentration on Days 4 or 8, but levels on Day 22 were higher (P<0.001) in pregnant cows. Mean milk progesterone concentrations were higher (P<0.001) in J than HF in Herd 2 on Day 8. Absolute milk progesterone concentration on Day 4 or 8 following AI did not predict the probability of pregnancy establishment, but the difference between milk progesterone concentration in the two samples was of predictive value on a herd, but not an individual cow, basis. Milk collection methods and breed effects need to be considered when developing milk progesterone concentration as a predictor of pregnancy establishment. Although the non-parametric analyses showed that non-pregnant animals tended to have lower milk progesterone concentration, the requirement for analysis of at least two samples will limit its use as a practical means to identify the subset of cows for which strategic progesterone supplementation might be considered.

GA, Verkerk, and KL Macmillan

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 95-97, 1998