Background- On most dairies, heifer rearing is one of the most overlooked and under managed assets on the farm. Replacement animals account for 15-20% of milk production costs, which represent the third largest component of production costs behind feed and labor. While it seems that everyone knows age at first calving (AFC) should be 24 months of age, it has been problematic attaining that goal. CAN WEST DHI reported the averages for AFC in 2012 were 26.4 months in BC, 26.5 months in AB, 27.0 months in SK, and 28 months in MB. Looking at these averages, does one think that calving heifers at 24 months of age is attainable? The answer is Yes! There are producers who are making full use of their heifer program to attain this goal.
Why do we want to aim for an AFC for 24 months? Numerous research trials has been done to understand the association between average daily gain (ADG), AFC, and latter animal health and lactation performance. Currently, research supports management and nutritional practices that encourage reducing average age at calving to 24 months of age. This target can be reached by implementing accelerated heifer rearing program with an ADG of 0.87 to 0.90 kg/hd/day from birth to 24 months of age. However, one needs to remember that during the first 2 months of life, a calf only gains an average of 0.80 kg/hd/day. So, you will need to play catch up after weaning!
On average, 45% of body weight and 70 to 80% of withers height is gained by 9 months of age. It is vital to focus on optimizing frame development and lean muscle growth during the first 9 months of life as efficiency of growth begins to decline as this heifer matures.
AFC and Dystocia
There are numerous benefits of accelerated heifer rearing programs later in the heifer’s life. Research has observed a correlation between dystocia and AFC. Heifers with an AFC of < 24 months trend towards a lower incidence of dystocia. Size and BW at first calving are significant factors affecting dystocia and the successful delivery of a live calf. Well-grown heifers will have minimal problems at calving. However, ease of calving can be adversely affected by the fatness of the dam. At equal body weights, animals with an AFC of >25 months have greater risk of being over-conditioned heifers with less skeletal growth, causing an increased incidence of dystocia than leaner, well developed heifers. This is due to smaller pelvic openings and larger than normal sized calves. Difficult calving increases the probability of other health diseases such as retained placenta, metritis, ketosis, and cystic ovaries.
AFC, Body Condition and Metabolic Diseases
Over conditioned animals can lead to further problems throughout lactation, causing an increased incidence of ketosis, acidosis, fatty liver, and lameness. Most of these problems are further amplified through reduced DMI and excessive body weight loss. Heifer BCS has a huge impact on later lactation performance. Heifers calving > 25 months of age are more prone to over conditioning. Compared to well-conditioned cows, over conditioned animals do not eat as much during early lactation, leading to increased body condition loss and other metabolic diseases. Such diseases include negative energy balance, ketosis, LDA, laminitis, etc. Accelerated heifer raising programs optimize protein and energy fractions through to 2 months prior to calving, reducing liver fat accumulation, negative energy balance, ketosis, and other postpartum metabolic problems.
AFC and Conception Rates
With everything working together, AFC can also be associated with conception rates during first lactation. Heifers with an AFC <24.5 months had improved conception rates of 19-32% during their first lactation when compared for heifers over 25 months of age. Interrelated factors such as body weight and condition score directly affect reproductive efficiency. Animals that are either under conditioned or over conditioned result in longer interval between initiation of breeding and pregnancy due to reduced estrus detection, cystic ovaries, and reduced immunity through previous health problems such as dystocia, retained placenta, ketosis, etc.
AFC and Milk Production
In regards to AFC, the interrelationship with milk production has been investigated the most. Results from a study involving DHI milk production and taped body weights are below:
Effect of AFC(in months) on First –Lactation Milk, Fat and Protein Production:
|AFC||Milk (kg)||Fat (%)||Fat (kg)||Protein (%)||Protein (kg)|
Kertz, Al. (2013). Age at first calving goal not realistic? Bottom Line of Nutrition:Dairy. Feedstuffs.
As you can see, results indicated as body weight increased from 408 to 612 kg, milk production increased 1000 kg. Past 680kg BW, milk production began to decline. AFC body weight influence these production traits. Animals above 25 months of age will have a greater body weight, affecting not only her overall health through lactation as previously demonstrated, but it will also impact her lifetime productivity.
Understanding the interrelationships between nutrition and management factors that affect heifer growth and health are important for optimizing animal production and health. With an AFC of 23 – 25 months, one can optimize metabolic, physiological and structural performance of dairy heifers, enhancing overall health, productivity and profitability.
Benefits to Producers
Accelerated development programs benefit the producer in 4 major ways:
- Increases the heifers ability to express her genetic size potential by improved efficiency of body size gain
Increases milk production and life time productivity due to more lean growth and less fat deposition, promoting optimal mammary development.
Improves animal health due to enhanced immune systems from superior nutrition. Lower growth rates during the heifer rearing stage are associated with common calf diseases such as diarrhea and respiratory diseases such as pneumonia. Diseases in early life affect later growth, health and first lactation performance.
Greater cost savings if heifers are grown correctly. Every day a heifer delays getting into the lactating herd results in a day of extra input costs(ex.feed costs).
All of these advantages together lead to healthier, stronger replacement animals, with greater genetic potential, ultimately driving your operation ahead.
References available upon request – Danielle_Kiezebrink@cargill.com