After calving season comes to an end, it won"t be long before breeding season begins. To ensure a successful breeding season, it is critical to monitor nutritional status of the cows by evaluating body condition score. If cows were thin at calving, it is going to be extremely difficult to get them to re-breed within 80 days of calving. Rebreeding within 80 days is necessary to be sure that they will calve on a 365 day interval so that they don"t become late-calving cows.
Breeding is a challenging time for cows because many key processes are taking place, including lactation, repair of the reproductive tract, restarting heat cycles, conceiving, and retaining the pregnancy. This period of time from calving to breeding equates to the highest nutrient requirements throughout the production cycle. It is important to remember that nutrient use is prioritized to maintenance first, growth second, lactation third and finally reproduction. Therefore, if the cow"s nutrient requirements are not being met, the first thing to be compromised or delayed is reproduction.
Nutrition & Body Condition
Steps can be taken to help ensure that cows are on a positive plane of nutrition, giving them the greatest opportunity to re-breed so that they have a calf every 365 days. First, they need to be in a positive energy balance or a body condition score of 5 for mature cows or 6 for first calf heifers at calving. If they are in this condition at calving, a 1200 lb cow that has a peak milk production of 20 lbs per day needs a diet that contains 58.7% TDN (total digestible nutrients). This can be achieved with a good quality grass hay or green pasture. This cow would also need a diet that contains 10.2% crude protein, which could also be achieved with a good quality grass/alfalfa mix hay or a good quality spring pasture.
The challenge is if cows are in poor body condition at calving and they need to gain weight. Because nutrients will tend to be diverted toward milk production, providing enough nutrition to meet requirements for both lactation and weight gain will be difficult. This will likely require the inclusion of high energy concentrate feeds, which takes more time, management and likely cost. It is easier to have them in the proper condition at calving and work to maintain that condition from calving to the breeding season.
Influence of Key Minerals
What about minerals? The key minerals that play roles in reproduction are phosphorus (P), copper (Cu), iodine (I), and manganese (Mn). A P deficiency will result in impaired reproduction. Phosphorus requirements change based on the size, stage of production and milk production of the cows, and is addressed in relation to calcium. For the 1200 lb cow, the P requirement is 0.2% of diet dry matter, while the calcium requirement is 0.3% of diet dry matter. Forage is a highly variable supply of P, therefore it is important to have the feeds tested to determine the level of P available to ensure the mineral supplement provided has an adequate amount to overcome any deficiencies. When considering mineral supplements, P is very important not only from the animal side, but also the economic side, as P is usually the most expensive ingredient in a mineral supplement.
- Copper is a challenging mineral due to antagonisms with other minerals tying Cu up. For example, sulfur and molybdenum will combine with Cu to form thiomolybdate compounds, which renders the Cu unavailable to the animal. In order to overcome this interaction, additional Cu, above the 10 ppm requirement has to be fed. A Cu deficiency can result in delayed or depressed estrus.
- Iodine is deficient in many locations, which is why it is critical to provide iodized salt to cattle. The requirement is only 0.5 ppm, but if this is not met, the result can be irregular estrus cycles and poor conception rates.
- Manganese is a micromineral that plays a key role in reproduction. Cows have a requirement of 40 ppm and if this is not met can result in depressed or irregular estrus, low conception rate, abortion, still births and low birth weights.
Most of the mineral concerns outlined above can be alleviated with a good mineral program or the inclusion of a trace mineralized salt into the supplement program. Work with a nutritionist or SDSU Extension Specialist to determine your breeding season nutritional needs.