It is always a good sign when fresh grass start to grow during early spring. However, due to the limited growth and volume, extra caution should be applied when the fresh grass is used as the sole source of nutrition for recently calved cows.
With the limited volume of grass, the animals can expend more energy as well as protein than what they are taking in and thus, lose body condition.
While it is very tempting to turn cows out on pasture when grass are growing during early spring, those short grass would not provide adequate nutrients to the cows for optimal performance. This is especially true when cows are coming out of gestation and into the period where they require the most nutrient.
Therefore, when feeding cows during spring, it is vital to ensure they received proper nutrition to maintain ideal body condition score and get re-bred. The number of calves you get the following year and how much they weigh will very much depend on the success of re-breeding your herd.
Nutritional Requirements By Cows
Nutritional requirements for the cows increase from gestation to the last trimester of pregnancy. It is the highest during lactation phase.
During lactation, the protein and phosphorus requirements for the cows also increases up to 60 - 70% compared to the requirements during last trimester. The requirements for total digestible nutrients (TDN), or energy, increases by an extra 15 - 25%.
It is vital to feed sufficient nutrients to the cows as they will affect the cows' milk production and reproduction performance. If you maintain the same feeding rate from gestation to lactation, it is definitely insufficient nutrients for the cows. This will cause the cows to lose body condition score and affect the reproduction performance.
Effects Of Feeding Insufficient Nutrients
Research shows that there is correlation between body condition score (BCS) at calving and how quickly the cows begin cycling and get pregnant. For cows that have a BCS of 6, 98% showed estrus by day 40 of the breeding season and 90% of the cows were confirmed to be pregnant by day 40. Compared to a BCS of 5, only 80% showed estrus and 65% confirmed pregnant. Such a massive difference by dropping a single point of BCS.
So if you have 100 cows for example, a single point drop in BCS from 6 to 5 at bleeding could equate to roughly 25 calves that are either born late or not born at all due to nutrition slipped post calving. As for the calves that were born later, they usually have less weaning weight.
Amount of energy provided to the cows will also affect the milk production and lactation length. Research shows that cows that consume 170 Kcal per metabolic body weight will maintain peak milk production for approximately 8.3 weeks with an average of 20.2 pounds of milk per day and will produce approximately 2,700 pounds of milk over 210 days. If additional energy is provided, at 290 Kcal per metabolic body weight, this resulted in the cow maintaining peak milk production for 10.9 weeks with an average of 24.2 pounds of milk per day and will produce approximately 3,700 pounds over 210 days.
Managing Nutrition During Spring
Although it is tempting to just feed the cows on green grass during early spring, the small volume is not enough to sustain the cows' energy requirement. The cows will run for green grass an burn energy searching for grass, resulting in energy deficit and thus a lost in BCS.
Although feeding supplements can help to regain the condition, it is often very costly as you are playing catching up and have to feed a large amount of supplements at a high cost.
A better solution is to provide free-choice hay and supplement early on when the grass starts to grow and continue and until it is lush and plentiful. Hay should be offered early on to ensure that the BCS of cows is at 6 during calving at no less than 5.5 when breeding.