Heifer fertility and carry over consequences for life time production in dairy and beef cattle

Abstract

The rearing period has a key influence on the later performance of cattle, affecting future fertility and longevity. Producers usually aim to breed replacement heifers by 15 months to calve at 24 months. An age at first calving (AFC) close to 2 years (23 to 25 months) is optimum for economic performance as it minimises the non-productive period and maintains a seasonal calving pattern. This is rarely achieved in either dairy or beef herds, with average AFC for dairy herds usually between 26 and 30 months. Maintaining a low AFC requires good heifer management with adequate growth to ensure an appropriate BW and frame size at calving. Puberty should occur at least 6 weeks before the target breeding age to enable animals to undergo oestrous cycles before mating. Cattle reach puberty at a fairly consistent, but breed-dependent, proportion of mature BW. Heifer fertility is a critical component of AFC. In US Holsteins the conception rate peaked at 57% at 15 to 16 months, declining in older heifers. Wide variations in growth rates on the same farm often lead to some animals having delayed first breeding and/or conception. Oestrous synchronisation regimes and sexed semen can both be used but unless heifers have been previously well-managed the success rates may be unacceptably low. Altering the nutritional input above or below those needed for maintenance at any stage from birth to first calving clearly alters the average daily gain (ADG) in weight. In general an ADG of around 0.75 kg/day seems optimal for dairy heifers, with lower rates delaying puberty and AFC. There is some scope to vary ADG at different ages providing animals reach an adequate size by calving. Major periods of nutritional deficiency and/or severe calfhood disease will, however, compromise development with long-term adverse consequences. Infectious disease can also cause pregnancy loss/abortion. First lactation milk yield may be slightly lower in younger calving cows but lifetime production is higher as such animals usually have good fertility and survive longer. There is now extensive evidence that as long as the AFC is > 23 months then future performance is not adversely influenced. On the other hand, delayed first calving > 30 months is associated with poor survival. Underfeeding of young heifers reduces their milk production potential and is a greater problem than overfeeding. Farmers are more likely to meet the optimum AFC target of 23 to 25 months if they monitor growth rates and adjust feed accordingly.

The association between age at first calving and survival of first lactation heifers within dairy herds

“…The present study represents one of the largest study to date, but it remains uncertain as to whether this truly reflects the UK situation, because a convenience sample was used to ensure data of sufficient quality. However, these findings are in agreement with a review article, which described larger data sets reporting a wide range in AFC within UK herds (Wathes et al, 2014).…”

Changes in the genetic level and the effects of age at first calving and milk production on survival during the first lactation over the last 25 years

“…Also, in most other countries an AFC around 24 months was found to be related with highest survival rate, but also with highest lifetime production: The Netherlands (Nor et al, 2013), Wallonia, Belgium (Froidmont et al, 2013), France (Ducrocq, 2005), Ireland (Evans et al, 2006;Berry and Cromie, 2009), United Kingdom (Wathes et al, 2014), Italy (Pirlo et al, 2000), Israel (Weller and Ezra, 2015), Iran (Nilforooshan and Edriss, 2004), Australia (Haworth et al, 2008) and Canada (Sewalem et al, 2005). However, with functional survival, that adjusts all cows to an average production level, no optimum AFC was found for survival.…”

“…In the literature, it has been suggested that animals calving in the optimal range of 22 to 26 months for AFC achieved highest lifetime milk yield and longest productive life, and resulted in highest profit per cow (Nilforooshan and Edriss, 2004;Froidmont et al, 2013;Wathes et al, 2014). But withinherd production level also affects survival.…”

“…This system might have affected culling reasons towards the end of the quota year (31 March), because farmers might have decided to cull more cows in order to avoid the penalty. How such a national regulation affected the culling, on a seasonal basis for example, has not yet been investigated.In the literature, it has been suggested that animals calving in the optimal range of 22 to 26 months for AFC achieved highest lifetime milk yield and longest productive life, and resulted in highest profit per cow (Nilforooshan and Edriss, 2004;Froidmont et al, 2013;Wathes et al, 2014). But withinherd production level also affects survival.…”

A Study of Dairy Heifer Rearing Practices from Birth to Weaning and Their Associated Costs on UK Dairy Farms

“…The rearing process is subject to high initial costs with revenue only beginning when the animal starts milk production [6]. The care of dairy youngstock during the initial period of development is crucial to ensure their survival in the milking herd, future milk production and their prospective earnings [7]. During the pre-weaning period, the calf undergoes fundamental physiological changes and is also subjected to additional stresses during this time such as regrouping and dehorning which can have negative impacts on growth and development.…”