Click here for a PDF version of this Calf Note
Introduction
Feeding roughage to calves often spurs debate among calf raisers. Some argue that including some roughage in the diet is important to rumen health and growth while others point to data that suggests that calves grow well with little or no dietary roughage. The subject of this Calf Note is to review some recent data regarding forage feeding to young, weaned calves.
Researchers at the Akey Nutrition and Research Center conducted four trials to evaluate graded levels of roughage in diets of weaned calves (Hill et al., 2010). Holstein steer calves were 8 weeks of age at the start of each 56-day study. Calves in each study were fed a common calf grower diet containing 20% CP and 12% NDF. The grower was based on whole corn, whole oats and a protein pellet with soybean meal as protein source. Calves were fed 0, 3, 6 or 9% chopped wheat straw (trial 1); 0, 5, 10 or 15% long alfalfa hay (trial 2); 0, 3, 6 or 9% chopped grass hay (trial 3); or 7.5% of the diet as long or chopped alfalfa hay (trial 4). Average daily BW gain and hip width change declined as amount of roughage in the diet increased.
Clearly, in these trials, increasing amount of roughage had a negative effect on growth. Others (e.g., Hill et al., 2009) suggest that little, if any, forage is required. Increasing amounts of roughage in the diet also contributes to gut fill, which makes it more difficult to determine exactly whether increased BW is increased body tissue or increased weight of undigested residue in the stomach and intestines. Stobo et al. (1966) reported increased gut fill and lower actual BW gain with increasing amounts of roughage in the diet of young, preweaned calves. A lot of research data suggests that calves don’t have a requirement for roughage in the diet per se, if the starter is properly formulated, manufactured and fed (Kertz, 2005).
Well, there are some data that suggest some hay can be good for calves. For example, Coverdale et al. (2004) reported improved performance of calves fed up to 15% of the DM as forage. McGavin and Morrill (1976) showed clearly that high grain diets can affect anatomical development of the rumen. Their landmark study revealed dramatic changes (damage) to the ultrastructure of rumen papillae caused by excess dietary carbohydrate. Hinders and Owen (1965) also reported that high grain, low forage diets can contribute to development of parakeratosis in steers. Thus, the concept of excess ruminal fermentation and ruminal problems seems to be a real concern. The key question may be not one of whether forage is necessary or not, but rather can a starter be formulated in such a way to minimize the risk of developing ruminal parakeratosis. In the study by Hill et al. (2010), the presence of whole grains (corn, oats) and the low amount of rapidly fermentable sugars probably reduced rates of ruminal fermentation. In addition, diets were well managed and available for ad libitum consumption. Water was available at all times. These management factors contribute to regular intake and smaller meals, which can also reduce the risk of rumen problems.
Roughage can be important to maintaining a normal, healthy rumen environment. When calves (or cows) consume hay, large particles float on the top of rumen liquid, forming a “mat” of hay that effectively strains incoming feed. This mat helps stabilize the rumen from large “slugs” of concentrate and helps promote cud chewing, salivation and maintenance of normal rumen pH. In the absence of forage, no mat is formed and the rumen contents can take the consistency of oatmeal. High rates of fermentation and buildup of acids (especially propionic and butyric acids) can cause excessive growth of the rumen papillae. In addition, the lack of fiber may impair removal of keratin from the outside of the papillae, causing them to clump together. So, seemingly, having some forage in the diet would be very helpful and promote greater intake and growth. Why, then, do we see some studies showing reduction in growth with increasing forage in the diet?
The answer relates to energy. When we replace concentrate (corn, oats, soybean) with forage – even good forage – we dilute the energy in the diet. Table 2 shows the difference in ME and NDF in typical concentrate ingredients vs. forages. Clearly, as we increase forage in the diet, we reduce energy and increase fiber. Limiting ME available will reduce growth and development of frame size.
The rumen of just weaned calves is still relatively small and rumen fermentation may not be fully functional. Thus, increasing dietary fiber could slow the rate of fermentation to the point at which the calf becomes limited in ME. This slows growth. The concept of physical fill (too much undigested residue in the stomach and intestines) limiting intake is a significant problem in calves fed too much fiber.
There appears to be an important balance between energy in the ration and amount of fiber. That is, if the concentrate contains ingredients that are rapidly fermented in the rumen to produce large amounts of acids in a short time, then the value of hay in the ration is increased. Feed management can also be such that calves tend to eat rapidly which can exacerbate the problem of low ruminal pH. On the other hand, ingredients not rapidly fermented in the rumen, or which can contribute some dietary fiber will slow the rate of ruminal fermentation and reduce the importance of forage in the diet.
In the studies conducted by Hill et al. (2010), the main carbohydrate ingredients in the diet were whole corn and whole oats. A comparison of this grower diet with that of Coverdale et al. (2004) is in Table 3. It’s possible that the feeds fed by Coverdale et al. (2004) were more rapidly fermented in the rumen. Their diets contained more molasses and wheat middlings, two ingredients rapidly fermented in the rumen. Grinding also increases rate of fermentation of carbohydrate in the rumen; thus the ground diet would be more rapidly fermented and change rumen VFA production, pH and other indices of rumen health. Indeed, concentrations of VFA in the rumen of calves fed the ground diet were greater than the whole diet in the study by Coverdale. Adding 15% grass hay to the whole diet reduced amounts of VFA in the rumen, suggesting that the forage slowed fermentation and potentially reduced the risk of digestive upset caused by large spikes in rumen acid.
In the end, the need for roughage probably depends more on the rest of the diet and management factors on the farm. Well formulated and well managed starter programs don’t require additional forage to optimize calf growth. Others may require it. Like many aspects of calf raising, there’s no “one size fits all” answer to this on-going debate.
References
Bull, L.S., L.J. Bush, J.D. Friend, B. Harris Jr., E.W. Jones. 1965.Incidence of ruminal parakeratosis in calves fed different rations and its relation to volatile ratty acid absorption. J. Dairy Sci. 48:1459-1466.
Hill, T. M., H. G. Bateman II, J. M. Aldrich, and R. L. Schlotterbeck. 2009. Roughage for diets fed to weaned dairy calves. Prof. Anim. Sci. 25:283–288.
Hill, T. M., H. G. Bateman II, J. M. Aldrich, and R. L. Schlotterbeck. 2010. Roughage amount, source, and processing for diets fed to weaned dairy calves. Prof. Anim. Sci. 26:181–187.
Hinders, R. G., and F.G. Owen. 1965. Relation of ruminal parakeratosis development to volatile fatty acid absorption. J. Dairy Sci. 48:1069-1073.
Coverdale, J. A., H. D. Tyler, J. D. Quigley, III, and J. A. Brumm. 2004. Effect of various levels of forage and form of diet on rumen development and growth in calves. J. Dairy Sci. 87:2554–2562.
Kertz, A. 2005. Role of forage in calf’s rumen development may be problematic. Feedstuffs. Vol. 77, March 14, 2005.
McGavin, M. D. and J. L. Morrill. 1976. Scanning electron microscopy and ruminal papillae in calves fed various amounts and forms of roughage. Am. J. Vet. Res. 37:497-508.
Stobo, I.J.F., J.H.B. Roy and H.J. Gaston. 1966. Rumen development in the calf. 1. The effect of diets containing different proportions of concentrates to hay on rumen development. Br. J. Nutr. 20:171-188.