Because dairy heifers are fed differently than beef heifers, it’s important to adjust their diets as they grow in order to bring them to an optimum age and weight at first breeding. Bovine Veterinarian conducted a Q&A with Susan Day, PhD, Land O’ Lakes Purina Feed LLC, on what it takes to successfully prepare the heifer for breeding, and what feeding mistakes to avoid.

Q: What are the typical growth targets we’re looking for at the time of first breeding for dairy heifers?

A: First breeding should be at 55% of mature body weight. Mature body weight is determined by averaging at least 10 3rd lactation cows in mid-lactation. This can be much harder to determine in cross-bred herds.

Post-calving, they should be at 85% of mature body weight (usually around 1,200 lbs. for the average Holstein). Also use body condition scories (BCS) at breeding. Heifers should be around 2.5–3 BCS at breeding (1–5 scale). Heifers allowed to get fat are harder to breed and don’t transition as well at calving.

Q: How much influence can proper nutrition have on reaching breeding growth targets in that 6–8 month window before first breeding?

A: The first six months of age are most efficient for building frame and efficient use of nutrients for growth. Calves in the first six months deposit more lean tissue per unit of gain.

In herds with more than one breed, heifers should be grouped by age rather than size. Large-breed heifers that are the same size as a small breed heifer will be at an earlier stage of growth, and their protein requirements will be higher. Grouping together will underfeed the large-breed heifers for protein and overfeed the small breed heifers.

Q: How much influence does proper nutrition pre-breeding have on heifer fertility? 

A: Heifer fertility should be very good as long as they receive protein, energy, vitamin and mineral requirements. There isn’t a lot of data to support use of additives on heifer fertility. Watch BCS to keep heifers growing in frame and not getting fat.

Make sure they are bred when they reach 55% of mature body weight. Post-puberty, heifers are very efficient at putting on fat, and can get fat quickly if left in the breeding group too long.

Q: What are some of the mistakes producers make regarding proper nutrition during this pre-breeding timeframe?

A: The first mistake is adding hay too early. Heifers don’t need hay until about 12 weeks of age, and it should be restricted to 0.5–2 lbs. in months 4–12. Young rumens are used to all-grain diets and don’t need the 50–50 forage:grain ratio recommended for lactating cows. Grain is a more nutrient-dense feed and is more efficiently digested by young heifers than forage, providing more energy and protein to the calf.

Another mistake is not feeding enough protein in the first six months. Calves in the first 12 weeks can efficiently use 20–22% crude protein starters, and even growers (months 4–6) should have at least 18% protein and decent quality hay.

One more mistake is putting pre-breeding heifers out to pasture with a mineral block. Heifers on poor-quality pasture can be deficient in protein and energy, which can impair breeding. These heifers should be supple-mented to maintain BCS. Body condition score should increase gradually in a heifer, starting at around 2.0 at birth, 2.6–2.8 at breeding and 3.5 at calving (1–5 scale).

Q: Does nutrition need to be consistent in those several months leading up to first breeding, or do a lot of producers try to play “catch-up” in the last month or two? 

A: Catch-up doesn’t work because heifers become more efficient at putting on fat as they age (% protein in gain goes down). So heifers won’t be as framey; they will just be fat if you try to put the weight on too late. Also, because of the efficiency of gain in the first six months, it makes economic sense to put the frame on them early and stair-step down the nutrient density as they get older.

Q: What happens if heifers are bred too early or too late?

A: Make sure you breed them when they are ready, not by an age target. Breeding too early will result in a small heifer that puts all of her energy into continued growth. Breeding too late doesn’t capitalize on the early input, and also may result in a fat heifer that doesn’t breed well or transition well.