Feeding grass to dairy cows
There have been few studies in the USA with cows fed predominantly perennial grass-based TMR’s. We have conducted a number of these grass feeding trials with medium to high producing cows. Rather than use forage to concentrate ratios, which favors the higher quality forage, rations were balanced for maximum NDF in the diet that would not limit intake. This allowed most cows to attain their intake potential with optimal ruminal fills. It also maximized the use of homegrown feeds, which had a favorable impact on farm nutrient balance.
Results from these studies:
1. Variations in fiber digestibility of grasses can account for differences in intake and milk production of cows fed diets similar in chemical composition but varying in ingredient composition (Cherney et al. 2002b).
2. Grass-based TMRs produced similar quantities of milk as those fed alfalfa-based TMRs (Jonker et al., 2002).
3. Dry matter intake increased as the portion of concentrate in diets increased, resulting in higher milk production in high tall fescue diets compared to high alfalfa diets (Cherney et al. 2002a).
4. Comparing starch vs. sugar supplementation of grass-based diets, the NFC source did not influence intake or milk production, but sucrose feeding lowered N utilization efficiency, when replacing a portion of the high moisture corn in the diet (Cherney et al. 2003a).
5. Tall fescue and orchardgrass TMRs performed as well as alfalfa, but grass will require more concentrate in the ration than alfalfa (Cherney et al. 2004).
Grass silage can produce as much milk per cow as alfalfa silage when rations are balanced. We observed no palatability problems with endophyte-free tall fescue.
Milk production per cow is a major factor in determining dairy farm sustainability/profitability. The inclusion of non-fibrous carbohydrates (NFC) in the range of 35 to 42% of dietary dry matter is seen as a popular way to increase energy density and thus milk production (Lykos et al., 1997). Balance of carbohydrates in the diet impacts milk production because it affects amount and ratios of ruminal volatile fatty acids produced, which in turn alters metabolism and partitioning of nutrients (Mertens, 1992).
In the above studies, the higher the fiber in the forage, the more concentrate in the diet. This resulted in generally higher intakes and higher milk production. Higher concentrate feeding results in a shift toward propionic acid production by ruminal microbes. Propionic acid is used by the mammary gland to produce lactose, responsible for milk volume, which accounts for milk production of cows fed grass being as high as those fed a lower fiber alfalfa. Differences in DM intake and subsequent milk production can also be attributed in part to differences in fiber digestibility and indigestible residue, resulting from lignin differences, as well as to differences in NSC (Cherney et al. 2004).