Previous research has demonstrated that feeding dried distillers grains with solubles (DDGS) has improved feed efficiency in ruminants (Anderson et al., 2006; Klopfenstein et al., 2008). The increased concentrations of fermentable fiber, and rumen undegradable protein found in DDGS compared to other feed sources such as corn and soybean meal are thought to be the cause of the improvement in animal production. Feeding DDGS has been well researched in beef heifers; however, there is limited research on feeding DDGS to dairy heifers. Dried distillers grains have been shown to be a replacement for corn and soybean meal in dairy heifer diets without causing changes in average daily gain (ADG) or negative effects on long-term performance (Anderson et al., 2015a).
Feeding DDGS to dairy heifers has been limited to high forage diets (Anderson et al., 2009; Anderson et al., 2015a). No research that we are aware of has examined the effects of replacing energy and protein from forage with energy and protein from DDGS in dairy heifer rations. In other words, research has not been conducted where DDGS has been the main concentrate in limit-fed dairy heifer rations. The high fat content of traditional DDGS, which is typically 10-15% ether extract, made this feeding strategy difficult. However, the development and availability of reduced-fat DDGS (RFDDGS), that has some of the fat removed through centrifugation, should allow it to be incorporated into the diet at much greater proportions
Very limited research has been conducted feeding RFDDGS to dairy heifers. Schroer et al. (2014) fed heifers that were approximately 5 months of age one of three diets: a control, DDGS, or RFDDGS diet. Heifers were fed for 12 weeks intake, feed efficiency, and growth was measured. However, this study only incorporated RFDDGS at 20% of the diet DM. Heifers fed the RFDDGS had similar ADG, feed efficiency, hip height, and withers height as heifers fed the control diet and DDGS. This demonstrated that RFDDGS did not negatively affect heifer growth and that RFDDGS is a viable feed source for dairy heifers (Schroer et al, 2014). Anderson et al., (2015a) limit-fed dairy heifers with diets of approximately 22% low-fat DDGS with ground corn compared to 33% full-fat DDGS or a control diet, with equal forage concentrations for six months and also found similar growth performance among treatments.
Age and size are the two frequently measured factors that play a role in puberty attainment. Dairy heifers usually reach puberty between 9 and 11 months of age at an average BW of 250 to 280 kg (Sejrsen and Purup, 1997). In beef heifers, an increase in ADG can influence the age and weight at which heifers attain puberty with heifers, with an increased ADG resulting in heifers being heavier at puberty (Short and Bellows, 1971). This increase in ADG may cause an increase in adipose deposition and an increase in leptin concentrations. Low ADG have been linked to decreased reproductive performances with decreased percentage bred, reduced pregnancies among animals bred, and higher pregnancy loss (Short and Bellows, 1971).
In dairy heifers increased prepubertal ADG has shown to affect milk production. Several researchers have shown that an increased ADG during the prepubertal period affected the development of parenchymal tissue in the mammary gland, resulting in decreased milk production (Hoffman and Funk, 1992; Sejrsen and Purup, 1997). This may be partially explained by IGF-1 receptors in the mammary tissues being less responsive when high energy diets are fed. This has been shown by reduced circulating growth hormones concentrations possibly as the result from negative feedback and an increase in circulating IGF-1 (Sejrsen and Purup, 1997).
We hypothesized that by using limit-feeding increasing the dietary concentration of RFDDGS would maintain heifer growth performance. However, we expected changes in metabolic hormones and profile specifically related to energy metabolism. We also expected some shift rumen fermentation as RFDDGS replaced forage in the diets. We also hypothesized that gain to feed and nutrient utilization would increase with increasing concentrations of RFDDGS.