The last trimester prior to calving is a critical time for the cow. Research indicates that pre-calving nutrition and management impact cow health and production, subsequent reproductive performance, and immune response in the calf. Approximately 70% of fetal growth occurs during this time, and nutrient requirements are increased accordingly. Energy requirements for a 1,200-pound cow increase from 9.3 Mcal/day during mid-gestation to 13.6 Mcal/day prior to calving (Figure 1). While the third trimester is certainly important, there is increasing evidence that cow nutrition throughout gestation can influence the future health and performance of her offspring.
Figure 1. Net energy for maintenance (NEm) requirements for a 1,200-pound cow.
This concept, and the associated term, “fetal programming,” was first reported over 20 years ago by an English doctor, who determined that human babies born to undernourished mothers experienced a variety of health problems later in life, including obesity, diabetes, and cardiovascular disease. In recent years, there has been an increased focus on determining the impacts of fetal programming on livestock production. In gestating beef cattle, nutrient deficiency may results from increased requirements, low diet quality, and lack of an adequate supplementation program. Evidence suggests that offspring of dams experiencing nutritional stress during gestation have increased incidence of mortality, metabolic disorders, reductions in postnatal growth, and reduced meat quality.
Important processes such as placental development, organ growth, and skeletal muscle development take place during the first two-thirds of pregnancy, and may be impacted by nutrient deficiencies experienced by the dam during this time. Intramuscular fat cells provide sites for marbling formation, and reports in the literature indicate that a decrease in nutrient availability to the dam can result in reduced muscle mass, animal performance, and ultimately marbling formation. A study conducted at South Dakota State University fed bred heifers at high, intermediate, and low levels of nutrition. Preliminary data indicated that differences in fat and muscle content of the fetus based on the cow’s nutrition. While results are inconsistent in terms of carcass quality response, there have been indications that supplementation of dams may lead to increased marbling scores in their offspring.
Influences on long-term growth and reproductive responses have also been reported. A three-year study conducted by Nebraska researchers found that heifer progeny from supplemented dams had greater weaning weights and prebreeding weights, and overall pregnancy rates for heifer progeny of supplemented cows was 93%, compared to 80% for heifer progeny of unsupplemented cows. In addition, the number of heifers calving in the first 21 days of the calving season was 28% greater for heifers from dams receiving supplement.