Goldilocks and the 3 Cows
All dairy cows mobilize stored fat for at least 3 weeks after calving to help support milk production. Metabolic problems such as ketosis and fatty liver are common if cows struggle to use the mobilized fat efficiently, reducing farm profits. Different management strategies during the dry period have been proposed to help minimize inefficient fat utilization around calving. Controlling body condition at calving to be between 3.00 and 3.50 is one such strategy because fat cows perform poorly. However, cows may store fat in their viscera (kidney and intestines) which is invisible to those who are body scoring cows. Just as belly fat (“pot belly”) in people has been linked to diabetes and heart disease, so cows that accumulate belly fat during the dry period may make them more prone to metabolic problems after calving. For many years pregnant dry cows have been fed diets above their energy requirements, especially during the close-up period, in order to prepare the ruminal microbes for high energy diets after calving and to compensate for decreasing feed intake during the last 1 to 2 weeks of gestation.
These diets are often heavy in corn silage or in grain if dry cows are fed weigh-backs from the lactating herd. Sometimes dry cows are ignored and do not receive enough groceries resulting in under-condition at calving and lack the energy reserves to support milk in the early weeks. Alternatively, feeding diets that include less corn silage and more low energy forages such as wheat straw may be “just right.” These “just right” diets (a.k.a. Goldilocks diets) allow cows to eat as much as they want without gaining weight.
At the University of Florida, 93 multiparous Holstein cows were divided into 2 groups and fed one of two TMRs from dry-off to calving, approximately 7 weeks. One diet was 58% corn silage and 8% wheat straw (excess energy) whereas the second diet was 37.5% wheat straw, 23% corn silage, and 6% triticale silage (maintenance energy). Wet brew, citrus pulp, canola meal, and minerals/vitamins were the other feed ingredients in both diets. At 2 weeks before calving, cows offered the high corn silage diet ate more TMR dry matter (27.3 vs. 24.7 lb) and so more energy (140 vs. 109% of their energy requirement) compared to the high wheat straw “Goldilocks” group. Interestingly, during the last 2 weeks of gestation cows fed the high corn silage diet dropped in feed intake twice as fast compared to the cows receiving the high straw diet. This rapid drop likely predisposes cows to metabolic problems upon calving.
Cows were fed the same TMR postpartum (45% corn silage, 14% ground corn, 15% soybean meal, 8% soybean hulls, 8% whole cottonseeds, 6% citrus pulp, and 4% minerals/vitamins). Cows were monitored closely for the first 15 weeks after calving. Cows fed the “Goldilocks” diet prepartum ate on average 2.6 more pounds of TMR dry matter daily throughout the first 15 weeks after calving (53.1 vs. 50.5 lb/day). The “Goldilocks” cows eating more feed produced 3.1 lb/day more milk (95.0 vs. 91.9 lb/day) but this increase was not statistically greater. Thus, cows eating the lower energy diet prepartum relied less on body energy reserves postpartum to sustain milk production. During the first weeks postpartum, these cows were in less negative energy balance, had 10% less fat in their blood, had less ketosis, and had 20% less fat in their liver as determined from liver biopsies. Overall, multiparous Holstein cows can be fed a single diet throughout the dry period that is matched to their nutrient requirements that will result in a healthier and potentially more productive performance after calving.
