There are two general approaches to keeping pregnant dairy heifers growing without becoming too fat, according to researchers from the USDA Dairy Forage Research Center and the University of Wisconsin.
One is to dilute the nutrients in a full-feed ration with bulky, low-energy forages. The other is to provide a more nutrient-dense ration, but at a restricted intake.
Wayne Coblentz, PhD, Research Dairy Scientist at the U.S. Dairy Forage Research Center near Marshfield, Wis., recently collaborated with fellow researchers at the University of Wisconsin to study the viability of feeding heifers more precisely with a limit-feeding strategy. They said this method is preferable to a bulky, ad-lib ration for a number of reasons, including:
- Greater residence time in the digestive tract;
- Slower passage rate;
- Greater dietary digestibility;
- Reduced fecal output; and
- Improved feed efficiency.
But there are disadvantages to this approach, too – mainly that heifers may rest less and vocalize more.
Coblentz and his colleagues set out to evaluate how feed bunk restrictions and push-up frequency affected the growth performance of pregnant Holstein heifers when fed a high-forage, nutrient-dense TMR composed (DM basis) mainly of alfalfa haylage (61%) and corn silage (38%).
In the study, published recently in the Journal of Dairy Science, a total of 128 Holstein heifers was enrolled in the 91-day trial, with groupings in pens of 8 heifers of similar weight. Each pen was equipped with 8 free stalls and 8 head-locking feed gates. The individual feeding gates provided some protection from adjacent, aggressive heifers.
Half of the pens were granted full access to the ration (100% stocking rate at the feed bunk), while the other half had two feed stalls blocked, creating more limited feed access with a 133% stocking rate at the bunk. Every heifer in both groups always had access to a free stall (100% stocking rate study-wide). Free stalls had a resting surface of mattresses covered with a shallow layer of dried organic solids, ensuring that heifers did not consume their bedding.
Half of both the full-fed and limit-fed pens had feed pushed up at 90-minute intervals, while the other half had push-ups take place every 3 hours (180 minutes) during the daytime. Feed was delivered to all groups once a day at 10:00 a.m., with most feed consumed by all groups within 9 hours.
Results of the study showed that heifers granted full access to feed had slightly higher final body weights, but total gain and average daily gain (ADG) did not differ significantly between the two groups. Feed push-up frequency also did not significantly impact the results.
The researchers concluded that heifers can achieve acceptable growth performance on high-energy, forage-based diets in limit-feeding programs that include moderate feed bunk restrictions. However, their conclusions are marked with the important caveat that other forms of stress must be minimized for those limit-fed animals.
“In many production facilities, the effects of overcrowding at the feed bunk cannot be separated from those potentially created by inadequate numbers of free stalls, inadequate area per heifer within the pen, or other forms of stress,” stated Coblentz.
The team cautioned that the study results should not be interpreted as a carte blanche directive to limit-feed heifers in all production situations. They believe the consistent results between the two groups could likely be attributed to heifers in each pen being sized similarly; heifers with feeding restrictions having adequate resting space in a clean, low-stress environment; head-locking feed gates likely providing passive heifers some protection from aggressive pen mates; and general minimization of other forms of stress.
