Many would argue that the two most important goals of heifer rearing for dairy producers are ensuring high milk yield in adulthood and reducing the age at first calving (AFC). Of course, in order to optimize 1st lactation yield, reduced calving age should not come at the cost of reduced body weight (BW). Indeed, it has been shown that improved growth of heifers under 6 months of age is associated with lower AFC and researchers have also found that improved pre-weaning performance can result in better 1st lactation milk yield. Pre-weaning average daily gain (ADG) can be improved by upping the level of nutrition, either through high levels of milk or milk replacer(MR) or through forage supplementation if calves are fed lower levels of MR. In order to see if pre-weaning forage supplementation had positive effects on diet digestibility, reproduction, growth and milk yield, researchers in Barcelona recently set out to see if adding forage to the pre-weaned diet of calves fed lower volumes of milk replacer would indeed have these desirable long-term effects.
Forage supplementation pre- and post-weaning or only post-weaning
60 female Holstein calves were given one of two treatments: The control calves (CON) were offered ground starter concentrate (19% crude protein, 19% neutral detergent fibre (NDF)], pre-weaning, followed by oats hay (68%) post weaning. The second group of calves (OH) were offered the same ground starter concentrate as the CON calves, but oats hay was supplemented both pre- and post-weaning. All calves had access to water ad libitum and were initially offered 6 L/d MR at 12% dry matter (DM) with a step-down process beginning at 28 days until being fully weaned at day 52. Until 65 days of age, forage and concentrate intake were recorded daily and BW was recorded weekly. Total tract apparent digestibility was determined two weeks after weaning. From that time until three months of age, heifers were offered the same concentrate and forage as previously, ad libitum. At 10 months of age, BW was measured. And, both age at breeding and milk yield at 1st lactation were also tracked.
Forage supplementation before weaning has positive effects pre-weaning, but not necessarily post-weaning
The OH calves had higher ADG, pre-weaning, due to greater starter concentrate intake (20% more than CON calves). This resulted in 24% more growth for the OH calves in the pre-weaning phase. Post weaning, while OH calves did consume more forage than CON calves, there was no difference in ADG or concentrate intake. There was also no difference between the two treatments in total tract apparent digestibility. In fact, the results indicate that young calves fed no forage pre-weaning adapt rapidly and are easily able to digest forage once offered. Additionally, although OH BW was greater at 65 days of age, both BW and ADG from two weeks post-weaning through 10 months of age did not differ. And, there was no significant difference between treatments in reproductive performance or 1st lactation milk yield or milk components.
While the pre-weaning improvement in growth was not maintained post-weaning, offering forage to calves pre-weaning does spur growth before weaning and could help in the transition to mixed diets. Additionally, ADG from 17 to 65 days of age was indeed positively correlated with energy-corrected milk yield. Therefore, the current study does concur with Soberon et al. (2012) who indicated that 22% of 1st lactation milk production variation could be explained by pre-weaning growth rate. While how one achieves that growth rate is certainly up to the individual farmer, one thing is clear: Better growth pre-weaning gives heifer calves a better start in life.