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Replacement Heifers

In the next section, we will cover replacement heifers. If we look at yearling heifers or about this time they will be going through puberty. And puberty is actually a function of weight. We know that nutrition affects growth, which should be targeted so that heifers have adequate weight to be pubertal at a certain age. Heifers actually reach puberty at about 65% of mature body weight. We want them to be at this weight by the beginning of the breeding season as yearlings. So that most, and by most we mean 90% or more, have reached puberty by the beginning of the season or the breeding season.

Let us look at a growth worksheet. Assume that we wean our heifers at 500 pounds on October the 15th. We assume that our cow herd has an expected mature body weight of 1,100 pounds. We would like to breed our heifers or our breeding season begins May the 1st. So that means that we will start calving somewhere around the 1st of February. And so between October the 15th and May the 1st is 198 days. Our pubertal body weight, which is 65% of mature body weight, would be about 715 pounds. If we subtract what the heifers weigh at weaning, which is 500, they need to gain 215 pounds over the next 198 days. Two hundred and fifteen (215) divided by 198 is about 1.1 pounds of gain per day to reach puberty by the beginning of the breeding season.

If you look at the nutrient requirements of heifers, higher to cows, but the trend is very similar.

Breeding TDN would be somewhat intermediate about 56% and crude protein about 9.6%. We have a bit of flushing or a higher nutrient plane at breeding. As we move through gestation to mid-gestation, TDN and crude protein would be the lowest, about 54% TDN, about 8% crude protein. About two to three months prior to calving, we would increase the TDN and the protein, TDN about 58%, protein about 8.4%. If we look at lactation and, realistically, about 10 pounds per day from these first-calf heifers, TDN should be somewhere around 63% and crude protein about 10.5%. And our target weight at calving, would be to have these heifers at about 85% of mature weight at calving.

Look at some management considerations for heifers. If we are supplementing or feeding the heifers, they need to be fed separately from the mature cows simply because they cannot compete. Socially, they are more immature than older animals or they cannot compete at the feed bunk. Nutrient demands, or TDN and crude protein concentrations, are slightly higher and if mixed with older cows, heifers generally have a lower body condition score at rebreeding causing a prolonged postpartum interval and reduced fertility.

We actually want to grow these heifers on a moderate plane of nutrition. We do not want to overfeed replacement heifers because fat or excess energy will be stored as fat and it is deposited in two detrimental places. One is in the pelvic area which can lead to increased dystocia at calving. The other is, fat is also deposited in the mammary gland which will decrease subsequent milk yield in future lactations. Sometimes we hear thoughts about limiting nutrition during gestation to reduce birth rate and therefore reduce dystocia. What happens if we limit nutrition during the gestation of heifers? We do see a small decrease in calf birth weight. And actually, counter to what most would think, we often see increased dystocia in heifers that are underfed. Generally, the calves are weaker at birth, we have higher mortality and higher morbidity. The colostrum quality will be lower. And milk production will also be lower. We also often see a longer postpartum interval to rebreeding and lower fertility.

What about creep feeding heifers during times of inadequate forage or poor forage? As with other calves, we often see an increase average daily gain of the animals simply because we are supplying additional energy and crude protein. You can reduce the body condition loss of the dams. Generally, we do it during times of poor forage quality or limited forage and usually this occurs somewhere around the end of the grazing season. What would we supplement these replacement heifers? Historical recommendation has been unlimited energy or a grain-based creep feed. However, some more current recommendations is some kind of protein-based supplement. For the same reason that supplementation of mature cows and we have positive associative affects if we offer a protein based supplement. If we offer a protein based creep supplement versus an energy based creep supplement, we will actually increase the forage intake of these calves. Even though we may offer a protein supplement, it is usually lower in protein than mature cows, somewhere around 16% to 20% crude protein. Another thing, this depends upon region of the US, we can often offer green creep to these calves and this may be meadow hay regrowth or barley, wheat pasture, something like that, so some type of green pasture to these calves. Should potential heifers be creep fed? One has to be cautious because the extra nutrition can cause increase fat deposition in the udder and decrease future milk yield. Usually we would only creep feed heifers during times of forage shortage emergencies, during drought, to get them to a normal weaning weight. We would never want to exceed normal weaning weights.

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