Factors influencing heifer survival and fertility on commercial dairy farms

Abstract

The average dairy cow survives only three lactations, reducing the availability of replacement heifers. Prenatal losses occur due to early embryonic mortality (about 40%), later embryo loss (up to 20% in high-yielding herds) or abortion (about 5%). A recent survey of 19 UK herds showed that 7.9% of calves were born dead and 3.4% died within 1 month. During the rearing phase, 6.7% of animals were lost before reaching first service at 15 months due to disease or accident and another 2.3% failed to conceive. Many potential replacements therefore never enter the milking herd. This severely limits opportunities for on-farm selection of breeding cows in addition to presenting a welfare issue and causing economic loss. The most profitable animals once lactation is reached combine good milk production with a regular calving pattern. Some aspects of performance are related to age at first calving (AFC), which in turn is influenced by heifer growth rates. Poorly growing animals required more services to conceive, calved later and subsequently performed badly. Optimum fertility and maximum yield in the first lactation were associated with an AFC of 24 to 25 months. However, heifers calving at 22 to 23 months performed best in terms of total milk yield and survival over the first 5 years, partly because good heifer fertility was associated with better fertility later. We have investigated some possible juvenile predictors of future performance. Low-birth-weight calves were more likely to come from either primiparous mothers or older dams (31 lactations) with higher peak milk yields, suggesting that the uterine environment may limit prenatal calf growth due to competition for nutrients with maternal growth or milk production. Linear trait classification scores for frame size show genetic correlations with longevity. The skeletal measures of height and crown rump length in 1-month-old calves was correlated to subsequent stature, and frame size was correlated to weight at 15 months. It may thus be possible to predict performance from simple size measurements as juveniles. Neither endogenous nor stimulated growth hormone (GH) release in 6-month-old calves were related to milk yield in the first three lactations, but size of a stimulated GH peak was positively related to milk energy values in the first lactation. Cows with delayed ovulation (.45 days) in the first lactation had a higher GH pulse amplitude and lower IGF-I as a juvenile. Cows that partition excess energy into milk in their first lactation may suffer reduced longevity.

Comparison of piecewise Weibull baseline survival models for estimation of true and functional longevity in Brown cattle raised in small herds

“…One explanation for these differences might be given by Bielfeldt et al (2006), who found out that the target age at first calving significantly differed between herd management systems. Wathes et al (2008) concluded from a review that the main factor when heifers conceive is the pre-pubertal growth rate, which is under both environmental and genetic effect.…”

Association between age at first calving, year and season of first calving and milk production in Holstein cows

“…The first lactation length was shorter with an AFC of more than 34 months. As suggested by Wathes et al (2008), poorly growing animals required more services to conceive, calved later and subsequently performed badly. Milk production during first lactation was maximised with an AFC between 22 and 26 months.…”

Additive genetic, non-additive genetic and permanent environmental effects for female reproductive performance in seasonal calving dairy females

“…Most research pertaining to the genetics of reproductive performance in dairy cattle has focused primarily on lactating cows (Royal et al, 2002; Kadarmideen conceive and 3.3% died or were culled due to infertility between 15 months of age and expected calving age. Of the heifers that failed to conceive at 15 months of age, some were reinseminated later in the year and subsequently calved for the first time older than 30 months of age (Wathes et al, 2008). Although management also affects reproductive performance, some of the results observed by Wathes et al, (2008) were also likely due to genetic effects.…”