Research Accomplishment Reports 2011

Metabolic Relationships in Supply of Nutrients for Lactating Cows

K.R. McLeod
Department of Animal and Food Sciences

 

Non-Technical Summary

Over 55% of the calcium, 17% of the protein, and 15% of the energy in the US diet are supplied by dairy products; thus, the US consumer is a major stakeholder for the project. Consumers want dairy products that are safe and inexpensive, but increasingly they also want an environmentally friendly dairy industry that promotes animal well-being. Natural resources are used efficiently when milk production per unit feed and per cow is high.

To efficiently produce milk, a cow must have a well-developed mammary gland and be able to supply the gland with the nutrients it needs. Nutrition in the first year of life affects mammary gland development, and nutrition around the time of calving and throughout lactation has a major effect on the health, productivity, and efficiency of cows. Feeding for optimal nutrient intake requires not only the provision of the necessary nutrients for milk production but also consideration to the effects of diet on mammary capacity and on appetite, health, and metabolic regulation of the cow.

Because feed costs account for half of all costs on a dairy farm, nutrition also significantly impacts farm expenses. This project considers all of these factors for optimal feeding. For example, if we could maintain current milk production while feeding diets with 4 percentage units less total protein, we would decrease N losses to the environment in the US by 470,000 metric tons per year and save US dairy farmers $1 billion per year in feed costs.

This type of progress only can be made if we take an integrated approach, combining quantiative measures of metabolites and genes involved in metabolic pathways with the use of mechanistic bio-mathematical models that accurately describe metabolism and production of cows. Refinement of the current nutrition programs will allow more exact formulation of diets for lactating dairy cattle and have immediate impact. Feed costs and environmental impacts from excess dietary nutrients will be reduced for dairy farmers. Consumers will benefit from both reduced environmental impacts of food production and lower prices due to increased supply and lower input costs. Consumers will also benefit from possible alteration of the fatty acid content and composition of milk fat, resulting in a healthier diet. A more strict scientific understanding of the dairy cow will allow scientists to further refine and leverage research efforts to improve efficiency.

2011 Project Description

Results from the production part of the experiment have been submitted for presentation at the national meeting of the American Society of Dairy Science.

2011 Impact

Ergot alkaloids in endophyte-infected grasses inhibit prolactin (PRL) secretion and may reduce milk production of cows consuming endophyte-infected grasses. We hypothesized that consumption of endophyte-infected fescue during the dry period inhibits mammary differentiation and subsequent milk production.

Twenty-five multiparous Holstein cows were randomly assigned to 3 treatment groups. Starting at 90-d prepartum, cows were fed endophyte-free fescue seed (control, CON; n=9), endophyte-free fescue seed and 3x/wk subcutaneous injections of bromocryptine (0.11 mg/kg BW; positive control, BROMO; n=8), or endophyte-infected fescue seed as 10% of the as-fed diet (INF; n=8).

Although milk yield of groups did not differ at -90 d prepartum, at dry-off (-60 d) INF and BROMO cows produced less milk (P < 0.05) than CON (averaging 86, 49 and 60 kg/d for CON, INF and BROMO cows). Throughout the treatment period, concentrations of PRL in the circulation were lower in INF and BROMO cows than CON cows (P < 0.05). Basal concentrations of PRL in venous plasma averaged 25.3, 2.8 and 3.7 ng/ml for CON, INF and BROMO cows, respectively.

Prepartum release of PRL was also reduced by ergot alkaloids, averaging 19.5, 9.2 and 1.1 ug PRL/ml*h (area under curve) for CON, INF and BROMO cows, respectively. At 10 d of lactation, when treatments were terminated, basal concentrations of PRL in plasma averaged 22.5, 1.6 and 1.4 ng/ml for CON, INF and BROMO cows, respectively. Three wk after treatment, circulating concentrations of PRL were equivalent across groups (P > 0.05). Gestation length did not differ between groups. Although treatment 4 wk prior to dry-off reduced milk yield in INF and BROMO cows, milk production in the ensuing lactation was increased 8% and 9% in INF and BROMO cows relative to CON (P < 0.05).

We reject our initial hypothesis, as data show that consumption of ergot alkaloids during the dry period increases milk production in the ensuing lactation. We propose that this effect is due to a reduction in PRL during the dry period, analogous to the production effect realized by exposing cows to reduced photoperiod (low PRL) during the dry period.