FROM THE FARM REPORT: WHAT INFLUENCES THE INTAKE OF HEIFERS IN THE POSTWEANING PERIOD?

Much emphasis has been on the calf period and improving growth and health of the preweaning period. However, the postweaning period is a very dynamic transition as heifers move to solid feed intake. Consumption of starter or grain and forage can be influenced by age, body weight, previous milk or milk replacer consumption, ambient temperature, availability of forage, water intake and others. How much do we expect them to consume and what is motivating intake during this age? However, what diet components in the postweaning period influence the heifer’s potential to consume the feed in front of her?

We recently did a trial with heifers that were nine weeks of age at the start and were fed ad libitum pelleted grain and a 2nd cut processed grass hay. We were testing the effect of two different crude protein levels (22 vs 26%). To facilitate the crude protein difference between 22 and 26% crude protein we used more wheat middlings, and as a result there was more NDF in the 22% CP pellet (24% NDF) compared to the 26% CP pellet (20% NDF). Otherwise starch, sugar, and fat were similar. The 2nd cut processed grass hay was ~15% CP, 55% NDF with a 61% 30 h degradability.

Figure 1.

Since we allowed ad libitum intake of the pelleted grain and hay, calves were able to consume what they wanted of each. Interestingly, we saw more influence of the NDF content of the pellet on intake in these animals than in the crude protein content. There was no impact on growth, and overall these postweaned heifers grew well, with an average daily gain of 3.3 lb/d (1.5 kg/d).

Figure 2.

On average these heifers consumed 3.2% of their body weight as dry matter intake (grain + hay). This is in line with previous work reported in a dataset by Quigley et al., 2021 showing that heifers from 8 to 17 weeks of age ranged from 2.5 to 3.5 % of body weight for dry matter intake. There was no difference in intake as a percentage of body weight between the different diets fed in this study, as shown in figure 1.

NDF intake as a % of body weight was different between the pellet with the higher NDF (24%) and the lower NDF (20%). Heifers that were fed higher NDF in the pellet averaged 0.85% of their body weight as NDF whereas calves that were fed lower NDF averaged 0.77% of their body weight as NDF. The intake of NDF as a percentage of body weight is shown in the figure 2.

In cows the typical benchmark for NDF intake as a percentage of body weight is ~1.2%. At this younger age, when heifers are fed pelleted grain and dry hay, it seems that this general benchmark does not apply. Rather for the 11 weeks or so that these heifers were fed the maximum intake that was achieved seemed to top off around 0.9% of BW. It would be interesting to compare this concept to other feeding scenarios like total mixed ration feeding. There seems to be some control of dry feed intake through different sources of neutral detergent fiber which may allow us to better predict dry matter intake of these young heifers.

— Sarah Morrison

morrison@whminer.com