A positive phenotypic correlation between milk protein percentage and reproductive performance in dairy cattle, especially during early lactation has been recently reported. The objective of this study was to quantify the relationship between milk protein percentage and different measures of fertility in Irish, seasonal calving, dairy cattle using data from experiments comparing strains of Holstein-Friesian cows under different feeding systems. The relationships between body condition score, milk production and fertility were also investigated. The data used in this study consisted of 584 lactation records over a 5-yr period. Principal component analysis and logistic regression was used to study the relationship between milk protein percentage and fertility performance of the cow. Greater milk protein percentage during the first 60 days post-calving was associated with better reproductive performance. The probability of a cow being submitted in the first 21 days of the breeding season increased with increased milk protein percentage during early lactation. Similarly, the probability of a cow becoming pregnant to its first service or to the whole breeding season also increased. Cows were classified as either high or low milk protein percentage based on their protein percentage over the whole lactation. Cows in the high milk protein group had a 7% greater conception rate compared to cows in the low protein percentage group. In conclusion, cows with higher protein percentage, especially during early lactation are submitted earlier in the breeding season, and have a higher conception rate. Physiologically, the shortage of glucose caused by negative energy balance restricts the synthesis of milk protein in the udder. On the other side, negative energy balance also causes the reduction of IGF-I, LH and oestradiol, which consequently delay the ovarian follicular development and finally reduces fertility. Therefore, there is a biological explanation for the association between milk protein percentage and fertility performance.

Prolificacy in sheep, under most types of flock management, may exert an overwhelming influence on profitability. Three major classes of sheep farming are found in New Zealand, namely Extensive farming, on high country and droughty areas where wool is the chief product, Store sheep farming, on harder hill country, where income is derived from sales of both wool and surplus stock, and Fat lamb farming, in the easier and improved areas, where sales of fat stock almost exclusively dictate the size of the income. In all three types, ewe fertility is of paramount importance. This investigation was undertaken as a pilot attempt to demonstrate, with more accuracy, the source of, or reason for, the additional lambs which result from flushing ewes, in as far as this practice may increase both ovulation rate and subsequent mortality or merely reduce mortality in developing ova at some as yet underdefined stage of early pregnancy. The nature of the experiment was such that a study of the time-relationships of ovum loss and embryo mortality at various stages in early pregnancy could be made. Thus the matings of 225 ewes in two separate mobs were observed and slaughter dates were measured for individual ewes from mating times. By this means a considerable collection of both field and laboratory data was made available for a study of comparative individual and group reactions to the flushing treatment applied.