Calving season is not only stressful and physically demanding for ranchers and hired hands but also stressful and nutritionally challenging to cows.The time period post-calving has the greatest nutrient demands a cow will experience during the entire production cycle.
Physiological demands post-calving are elevated to support lactation and repair the reproductive tract. Adequate nutrition in the form of energy and protein to the cow is important for uterine involution and critical for colostrum and milk production. Thus, plane of nutrition is an important part of cattle management throughout the production cycle. Pre-calving nutrition is probably more important than post-calving nutrition in influencing postpartum interval length; however, post-calving nutrition can’t be taken for granted. Factors that influence when and how much post-calving supplementation is needed include nutrient requirements, weather, body condition score (BCS) and cow age.
Factors influencing nutrient requirements
The beef cow utilizes 70% to 75% of dietary energy for maintenance, and the residual is used for pregnancy, lactation, activity and adaptation to the environment. Producers that are increasing the mature cow size of their herd should recognize the increased energy requirements of larger cows.
Another important consideration on nutrient requirements is milk production. As milk production potential increases in beef cows, cow maintenance requirements during gestation and lactation increase. Lactation adds a considerable increase in the energy requirements of a cow post-calving. Other factors influencing the amount of energy and protein to meet the nutrient demands of a cow include weather, BCS and age.
In regards to age, younger lactating females that are still growing have an increased energy and protein requirement to support additional growth compared with mature cows. Separating young females and mature cows is an effective management strategy to better match supplements to requirements according to cow age.
Body condition score and postpartum energy intake
Proper nutrition and adequate BCS at calving can reduce the postpartum anestrus period and reduce the postpartum interval. Body condition scoring is an effective management tool to estimate the energy reserves of a cow. Traditional recommendations suggest cows need to be nutritionally managed at a BCS 5 or greater at calving for optimal reproductive performance. However, within any year, the normal variation among animals in a herd will result in some cows being below and some above the average BCS of the herd at any given time. This variation may reflect differences in stage and level of production (especially milk), cow size (maintenance energy requirements) and fleshing ability.
A constraint to reproductive efficiency in beef herds is the duration between calving and resumption of estrus post-calving. This is especially true for young cows that are also trying to grow while lactating for the first or second time.
To maintain an annual calving interval, cows need to recover from calving and conceive within 80 to 85 days post-calving. Cows that calve in a thin BCS (BCS 4 and less) have been shown to have a longer postpartum interval and reduced pregnancy rates. Although calving BCS can influence rebreeding and performance of cows, it does not mean thin cows will always result in decreased reproductive performance.
There is evidence that thin cows at calving can achieve a high pregnancy rate. If thin cows are not nutritionally challenged after calving with inclement weather conditions or nutritional restrictions, reproduction may not be reduced (Table 1).
A large impact on reproduction is direction and magnitude of bodyweight change post-calving and through breeding. The goal is to shorten the period of weight loss by increased nutrient supply so that positive bodyweight gain can be initiated as soon as possible, and the cows can start cycling.
If nutrient intake is decreased postpartum in overconditioned beef cows during late gestation, cows with greater BCS at calving may exhibit a greater bodyweight loss and decreased reproductive performance.
Supplementation strategies
Understanding how stress (physiological or environmental) influences nutrient requirements is a good starting point to know when to intervene with supplement, which needs to be evaluated depending on stage of production, weather, BCS and age. Also, identifying the quality and quantity of the basal diet post-calving should be evaluated annually and be taken into consideration when trying to evaluate which supplements may produce the desired results.
Post-calving is the most challenging time to increase BCS of cows because of the nutrient demands of lactation, but if cows are thin at this time, additional protein and energy are required in improving BCS. Because of the nutritional demands of lactation, it can be difficult to get cows to gain bodyweight economically post-calving. This is due to nutrient requirement being the greatest up to approximately day 60 post-calving, which also coincides with the start of breeding. Underestimating milk production in the cow herd can result in inadequate nutritional inputs and may decrease reproductive performance.
Establishing a flexible nutrition program to put in place post-calving will help alleviate some stress from the calving season for cow-calf producers and less stress for the cows. Increasing the energy content of the diet post-calving will help decrease the postpartum interval and increase reproductive success during the breeding season.
