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For the high producing cow in the first three weeks after calving, it is often difficult to meet her energy requirements for lactation with her feed allocation, since her intake potential is depressed. Thus, she loses weight and condition because her genetically and hormonal-controlled milk yield has to be supplemented from her energy reserves. The negative associated affect is that oestrus and conception may be delayed. Nutritionists battle with this problem and follow various approaches to try and increase energy intake such as fat supplementation, more starch in the diet, feed additives such as monensin (Rumensin) to increase efficiency of energy utilization etc. Although benefits are mostly shown, there are also negatives which have to be controlled or balanced. This study reports on increased starch in the diet with or without the addition of monensin. The authors are Dr M.M. McCarthy and co-workers with two papers in the Journal of Dairy Science, Volume 98 of 2015, respectively pages 3335-3350 and 3351-3365. The respective titles of the papers are: Performance of early-lactation dairy cows as affected by dietary starch and monensin supplementation andMetabolism of early-lactation dairy cows as affected by dietary starch and monensin supplementation.
The objective in the first study was to evaluate the effect of dietary starch content and monensin supplementation throughout the transition period (before and after calving) and into early lactation on production performance of dairy cows during early lactation. Before calving, 21 first-calf heifers and 49 older Holstein cows were fed a common controlled-energy close-up diet with a daily top-dress of either 0 or 400 mg monensin per day. From day 1 to 21 after calving, the cows were fed a high-starch (26.2% starch, 34.3% NDF), or low-starch (21.5% starch, 36.9% NDF) total mixed ration with a daily top-dress of either 0 mg or 450 mg monensin per day. These feeding treatments were continued during day 22 through 63 of lactation.
The cows fed the high-starch diet from day 1 to 21 after calving had higher early-lactation milk yields compared with the cows receiving the low-starch diet, but the high-starch cows also had lower percentages of milk fat, true protein, lactose and total solids during the same period, resulting in similar yields of energy-corrected milk (ECM) between starch treatments. The cows fed the high-starch diet had higher early-lactation dry matter intake (DMI) and lost less body condition score during days 1 to 21 after calving, which contributed to improved after calving energy balance. No effect of starch treatment was observed on apparent total-tract dry matter or starch digestibility, although the cows fed the low-starch diet had greater apparent total-tract NDF digestibility compared with the cows fed the high-starch diet. The cows fed monensin had higher DMI and higher milk yields during the first 63 days of lactation. However, all cows had similar yields of ECM because of trends for lower milk fat content during early lactation. In part because of similar yields of ECM between these treatments and higher DMI for cows fed monensin, ECM per DMI during the first 63 days of lactation was not affected by monensin treatment. There was also no effect of monensin treatment on apparent total-tract dry matter, NDF, or starch digestibility.
Overall, the results show that the cows fed more glucose-producing diets in early lactation (that is high-starch or monensin) had increased milk yield and DMI during the immediate after- calving period, indicating that diets with greater glucose-producing capacity do not have detrimental effects on early-lactation DMI. This is positive, but as high starch diets may cause acidosis, managers should be careful. Monensin, of course, can assist wih control of acidosis.
The objective of the second study was to evaluate the effect of these dietary starch and monensin treatments on the metabolism of the cows during early lactation. The results show that cows fed the high-starch diet had higher plasma glucose and insulin and lower non-esterified fatty acids (NEFA) than the cows fed the low-starch diet during day 1 to 21 after calving. The cows fed low-starch had elevated early-lactation β-hydroxybutyrate (BHBA) compared with the cows fed the high-starch, indicating that the cows on low-starch had to mobilise more body energy than the cows on high-starch. There was no effect of monensin on the after calving plasma NEFA, but the cows fed monensin had higher plasma glucose compared with control (no monensin) cows. The cows fed monensin also had lower plasma BHBA compared with the control cows. Starch treatment had no effect on overall liver triglyceride content. However, the first-calf heifers fed monensin had increased liver triglyceride content compared with the control first-calf heifers and the older cows fed monensin had decreased liver triglyceride content compared with the control older cows. The older cows fed the low-starch diet with monensin had higher liver glycogen contents than the older cows fed the low-starch diet without monensin. Monensin treatment had no effect on older cows fed the high-starch diet. There was no effect of starch or monensin on the capacity of the liver to oxidize (utilise) propionate and the effects of starch on the production of glucose from other metabolites were not significant. However, the cows fed monensin tended to have a greater capacity to convert propionate to glucose than control cows. Supplementation with monensin increased the ratio of glucose to carbon dioxide, which indicates that the cows fed monensin had a greater propensity to convert propionate to glucose.
Overall, the cows fed more propionate-forming diets in early lactation (high starch or monensin) exhibited improved energy metabolism during early lactation, substantiating the observations found in the production study.