Effect of feeding and bodyweight on growth, milk production and fertility

This paper forms some of the basis of the Dairy NZ table of heifer growth stage live weight targets. It shows the acceptance of pasture based heifer rearing programmes having a lower first calving live weight.

With the genetic advances made in the last twenty years it has been agreed that heifers need to be grown to a better weight as they enter the herd to ensure their genetic potential is met.

Historical studies have shown that accelerated growth pre puberty can result in reduced mammary tissue development. But further analysis of the studies and adjustments made for breeding worth give inconsistencies in the results. The paper reports heifers reared at 0.6-0.8kg LW/day pre puberty there was no effect on milk production. It could be that the higher bodyweight at calving offsets any negative effect of accelerated growth pre puberty. The report did identify that postpubertal accelerated growth systems, even in grazed systems, does induce greater intensity of mammary development and in the first lactation increase milk production.

So the question is does the grazed system actually suit the proven method of stair-step compensatory growth patterns?

K. A. Macdonald, J. W. Penno, A. M. Bryant, and J. R. Roche (2005) Effect of Feeding Level Pre- and Post-Puberty and Body Weight at First Calving on Growth, Milk Production, and Fertility in Grazing Dairy Cows, J. Dairy Sci. 88, 3363–3375, 

Abstract

Heifer growth rate and BW at first calving are regarded as important benchmarks in dairy farm management (Sejrsen and Purup, 1997; NRC, 2001). Increased growth rate can reduce the time the heifer spends in a nonproductive state (Capuco et al., 1995; Sejrsen and Purup, 1997), but excessive prepubertal growth rates have been linked to reduced milk production (Harrison et al., 1983; Sejrsen et al., 1983; Ingvartsen et al., 1988; Sejrsen and Purup, 1997). In addition, recommendations on optimum first-calving BW vary widely.  In high concentrate intensive feeding systems, it is recommended that Holstein-Friesian (HF) cows achieve 540 to 650 kg of BW before first calving (Keownand Everett, 1986; Heinrichs, 1993; Hoffman, 1997); a more modest first-calving BW is accepted in pasturebased systems (490 to 550 kg; McLean and Freeman, 1996; Holmes et al., 2002).