Assessing the Association of the Level of Milk Production with Reproductive Performance in Dairy Cattle

Abstract

Abstract. There is much debate about possible antagonism between high milk production and reproductive performance. This paper reviews methods of measuring reproductive performance and the association of the level of milk production with pregnancy rate at the herd and individual levels. The main question is whether fertility (the capacity for reproductive function and successful pregnancy) of dairy cows has in fact declined, as opposed to the success of management systems and people at meeting the metabolic, nutritional, housing, and social needs of increasingly productive animals but with no less inherent capacity to achieve and maintain pregnancy; and if fertility really has diminished, the extent to which this decline is caused by increased milk production. There is no doubt that production per cow has increased, but it is unclear how much of this increase can explain the apparent decrease in fertility. It is important to separate the biology of reproductive function from the effects of economically based management decisions about culling and continuation of breeding. Most traditionally-used measures of reproductive performance (calving interval, conception rate, non-return rate) are incomplete or severely biased outcome measures. Both herd and cow-level data should include as much information as possible on confounders of the relationship of production with reproduction. Population or herd-level data should not be used to make inferences about individuallevel associations. Considering the quality of data and analytic methods in the published literature, it is not clear if there is any association between higher milk yield and the probability and timing of pregnancy, either among cows at various levels of production in a population at one time, or with increasing production over time. Key words: Epidemiology, Management, Milk yield, Pregnancy rate, Selection (J. Reprod. Dev. 56: S1-S7, 2010) ilk production and reproductive performance are two major determinants of dairy cow profitability. There is much debate among dairy producers and researchers about possible antagonism between high milk production and reproductive performance. Some worry about genetic selection for fertility or ask whether management can meet the needs of cows for both high production and timely and efficient pregnancy. This paper reviews methods of measuring reproductive performance and the association of the level of milk production with pregnancy rate at the herd and individual levels.Many papers refer to a decline in fertility in dairy cattle over the last 20 to 30 years but valid primary data to support this assertion are scarce. While there are reports from 50 to 80 years ago expressing concern about reproductive performance and the effect of increasing production on it, it seems that measures of reproduction in large datasets only began to decline in the mid-1970's to mid-1980's [1-3]. In fact, very recent data suggest that the trend in the USA in some of the same measures has begun to improve [4] (despite ongoing increases in prod...

Short- and long-term effects of high milking frequency during the first 21 days of lactation on production and reproductive performance in high-lactating cows

“…The further increase in milk yield due to HMF might be assumed to depress reproductive performance even more. Nevertheless, some studies have reported that fertility is not necessarily impaired by increased milk production at either the individual cow or herd level (Lopez-Gatius et al, 2006;Lof et al, 2007;LeBlanc, 2010). Our results support this statement because we did not find any negative effect on reproductive parameters such as days to first insemination, days to pregnancy or conception rate for first insemination.…”

Effect of bull, diluter and LDL-cholesterol concentration on spermatozoa resistance against cold shock

“…The issue of cattle fertility was intensively studied in recent years from cow point of view and eff ects on their reproductive performance (Doležalová et al, 2013;Roche et al, 2011;Hanuš et al, 2010;LeBlanc et al, 2010). However, cow's reproduction results are also aff ecting by male component which is represented by the fertilization ability of bull ejaculate.…”

Factors associated with 56-day non-return rate in dairy cattle

“…Selection process for milk yield increases blood concentrations of somatotropin and prolactin, stimulators of lactation, and decreased insulin, a hormone that is antagonistic to lactation and may be important for normal follicular development (LeBlanc, 2010). Therefore, reproductive performance is compromised primarily through delayed ovarian activity and also reduced conception rates by high milk yield.…”