An investigation into the practical application of the radioimmunoassay (RIA) test of milk progesterone to improve artificial insemination (AI) management in diary cattle

Abstract

Reproductive performance is one of the most important factors determining profitability in dairy herds (Lamming & Darwash, 1998). Current intercalving intervals (an indicator of reproductive performance) are generally too long for optimal milk production and the number of progeny born per year. These long intercalving intervals may be associated with managerial influences, such as breeding policy or the detection of oestrus or fertility problems, such as acyclia or "repeat breeders" i.e. the problem cow syndrome. Esslemont and Kossaibati (1998) suggested repeat breeding to be caused by an inadequate supply of the hormone progesterone, during the luteal phase of the oestrous cycle and Erb eta/. (1976) found that unsuccessful inseminations were often accompanied by asynchronies in the hormonal profiles. Levels of and patterns of especially progesterone secretion could thus be one of the underlying causes of repeat breeding in problem cows. The hormone progesterone is produced by a transient organ, which develops in the ovary, after ovulation, called the corpus luteum (CL). The CL functions for a specific period of time (19-22 days after AI) and, if conception does not occur, undergoes regression. If conception does occur, however, the CL continues to function and secrete progesterone throughout the gestation period. Thus the concentration of progesterone in the body flu ids can vary according to the reproductive status of the animal (Ball & McEwen, 1998) and the measurement of progesterone levels in plasma is a specific indicator f . IERSfN 0 luteal functton (Becket a/., 1996). The presence of progesterone in cow milk was first Williams (1991) and Bloomfield eta/. (1986). Laing and Heap (1971) realised that, if progesterone levels in milk were closely correlated wi h those in the plasma, · great benefits would accrue to physiology, because of the relative ease of collecting milk rather than blood samples. Progesterone in milk was positively identified by Heap eta/. (1973) and high correlations (r = 0.91) with progesterone levels in milk and plasma were recorded by Hoffman et a/. (1976) and Peters (1984). This led to the development of sophisticated techniques to measure milk progesterone levels by Cox eta/. (1978) and identify the physiological status of the animal. As a result milk progesterone profiles and individual milk sample measurements can now be used to monitor the luteal and hence ovarian activity of pregnant cows (Pursley eta/., 1997b). Milk progesterone analysis may thus been seen as a most convenient method of monitoring ovarian activity in dairy cows and the possibility to use this technique as a routine procedure for pregnancy diagnosis service to commercial dairy producers may be possible. The objective of this study was to: a) test the accuracy of pregnancy diagnosis with the aid of a milk progesterone concentration assay b) use the milk progesterone assay to evaluate the progesterone profiles of cows classified as problem (low fertile) cows and c) determine a strategy to solve the incidence of problem low fertile cows, relating to information acquired from the milk progesterone assay.