Heifer Development

Chapter 28
Heifer Development: From Weaning to Calving

Ricardo Stockler

Veterinary Medicine Teaching and Research Center (VMTRC), University of California Davis, Tulare, California, USA

Performance during first lactation is the best indicator that a successful rearing program has been implemented. The typical guidelines to consider are (i) optimum age at first calving should be around 22–24 months of age; (ii) excessive rate of weight gain prior to puberty directly affects performance, reproductively and productively; and (iii) never underestimate the costs associated with rearing programs.

There are many alternatives with regard to housing and delivery of feed to recently weaned heifers. From pasture to confinement, it is imperative to avoid overcrowding, and to move heifers out of the hutches in small groups of 5–10 head at a time.1,2 This is the beginning of a system where the heifers experience the most stressful time as a group. The main advantage of having a small group is that this allows the heifers the opportunity to adjust to diet change, pathogen challenges, and proper growth. Ultimately, the goal is to raise healthy heifers that reach the breeding group as homogeneous and balanced as possible; however it is imperative to keep in mind that when calves are grouped, the risk of diseases such as respiratory conditions and diarrhea, specifically coccidiosis in this age group (>30 days old), increases.

A palatable concentrate diet (same as that being fed in the hutch) should continue to be offered during the first 2–3 weeks after grouping, followed by a change to a heifer grower ration with inclusion of a coccidiostat product, either an ionophore or a sulfonamide. In addition to the heifer grower ration, early cut forages are preferred for the recently weaned younger heifers, as they are higher in energy and protein and lower in fiber. High-fiber products should be avoided in young calves as the rumen–reticulum is still under development, and unable to fully digest fiber-rich diets.1 The major goal when it comes to feeding is to sustain uniform weight gain and growth, which will allow the heifer calf to attain puberty and thus breeding at the recommended age. The National Research Council3 suggests an average daily gain of 0.7–0.8 kg, assuming that a healthy calf is being raised in a thermoneutral environment. In addition, Drackley4 clearly states that a growth rate of 0.9 kg/day is achievable and does not affect mammary development, but needs to be adjusted to improve animal health and farm productivity. Therefore dry matter intake (DMI) must be managed properly based on environmental conditions. DMI should be increased when temperatures are below 15 °C; failure to provide extra energy can result in decreases of up to 0.2 kg/day of average daily gain.3 If forage availability is not an issue, heifers raised on pasture should not have problems reaching the goal suggested by the National Research Council, despite the extreme variability in quantity and quality. Special attention should be paid to the trace and major minerals, as supplementation may be warranted depending on the region and season.

Body weight is directly correlated to puberty as well as first-lactation milk yield. An easy rule of thumb to remember is that target body weight at initiation of breeding should be around 55% of mature body weight and 82% of mature body weight at calving. It is important to stress that growth rate is by far the major contributory factor to a successful breeding heifer program.5 Monitoring body condition (weight gain) provides valuable field information with regard to weight changes. One body condition equals 54 kg of body weight.6 Table 28.1 summarizes the ideal body condition score at different production stages.

Table 28.1 Target body condition score and production cycle.

Body condition score (1–5 scoring system)
Calving 3.5
Peak milk 2.75
Mid lactation 3.0
Dry-off 3.5
Replacement heifers
6 months old 2.75
Breeding age 3.0
Calving 3.5

Heifers express their first estrus at 9–12 months of age and weight of approximately 280–300 kg.2 The identification of heifers that are suitable to be bred is essential. Individuals not reproductively sound, underdeveloped, or freemartins should be removed as soon as possible. Therefore it is recommended to move heifers into the breeding pool 2–3 months prior to expected initiation of breeding, so estrus and potential problems can be identified. The diet offered should provide a stable rate of gain, since excessive growth at this point is not necessary and wasteful. Springing heifers should be fed ingredients similar to the lactating group, with good-quality forages and a limited amount of concentrate (1% body weight), with the intention of a smooth transition, which in turn supports a high DMI immediately after calving and optimum peak milk. Close attention should be paid to the sodium and potassium concentration in the diet as it is known to be one of the causes of udder edema after calving.

A summary of the optimum target body weight and height as well as average daily gain for different age groups of Holsteins and Jerseys is summarized in Table 28.2. It should be noted that these are raw guidelines and the numbers may vary according to region and type of system being utilized to raise replacement heifers.

Table 28.2 Summary of target body weight (BW), height (H), and average daily gain (ADG) for different age groups of Holstein and Jersey heifers.2,5

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Aug 24, 2017 | Posted by in GENERAL | Comments Off on Heifer Development

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Weight (kg) Height (cm)
Age (months) Holstein Jersey Holstein Jersey ADG
6 160 113 100 90 0.7–0.8 kg/day
12 295 204 119