Source: Ministry of Agriculture, Food and Rural Affairs
The backbone of a cow calf production system is the selection and integration of heifers into the beef herd. The replacement rate varies considerably between farms but on average lies between 10 to 20%. The decisions around which cow to cull ranges from age of cow, breeding success, calf quality, rearing success, temperament of cow, cow health etc. In the majority of cases, the age of the cow is the number one determinant on which cow should be culled.
Since the replacement heifer is the foundation of a productive cow herd, the choice of heifer and her development can greatly impact the economics of the farm operation through her genetics, future performance, and longevity. Time of first calving has a major influence on life time productivity, which is one of the most important traits to consider. Research has consistently shown that targeting first calving at 24 months maximises lifetime productivity, provided the cow continues to produce a calf each year. Research from Oklahoma State University College of Agriculture Sciences showed that heifers calving at 24 months produced 330 lbs of calf more over their lifetime than heifers calving at 36 months.
To calf at 24 months, heifers must be bred by 15 months of age. The onset of puberty in cattle is determined by weight, age and breed. Weight is the major factor. The age at which puberty occurs is breed dependant with larger, later maturing breeds coming into puberty later than smaller, earlier maturing breeds.
Table 1. Weight (lbs) at which 14 – 15 month old heifers of different breeds reaches puberty.
Source: J. Field, OMAFRA
Table 1 shows the effect of weight on the % of heifers in a herd at 14 – 15 months of age which show first heats, (onset of puberty). It demonstrates that earlier maturing breeds, i.e Angus, Heredford, reach puberty at a lighter weight than larger framed breeds, i.e. Charolais, Simmental. Farmers should bear these target weights in mind when selecting heifers to breed. Larger framed breeds must weight heavier at the target breeding date, i.e 15 months, compared to smaller framed breeds. Feeding the correct nutrition to heifer calves, taking into account breed, is important to ensure heifers reach their target weight by 15 months of age.
Replacement beef heifers should attain 65 to 70% of their potential mature weight by the time they are bred at 14-15 months of age. From weaning to first breeding, heifers should gain an average of 0.56 kgs to 0.80 kgs, (1.25 lbs to 1.75 lbs), per day or 115 to 160 kgs, (250 to 350 lbs), total (depending on breed). For most breeds and crosses, heifers should weigh between 300 to 390 kgs, (650 to 850 lbs.), at breeding time.
Lifetime productivity rates are affected by feeding management during critical phases. Research has shown that energy intake in excess of requirement can lead to the infiltration of fat into the developing udder which may restrict milk production in those heifers as cows later in life. Poor milk production leads to poor calf performance and earlier culling than planned for that animal.
Table 2. Nutrient Requirement for Replacement Heifers (growing at 1.25 lbs per day).
Medium Framed Heifers
Source: J. Field, OMAFRA
Table 2 shows the ideal nutrient requirement of growing heifers at various body weights. Medium framed heifers have a lower feed requirement at the same weight as large framed heifers. Producers must be conscious of the frame type of heifer on their farm to avoid underfeeding or overfeeding.
Producers should plan breeding of heifers at least 3 weeks before breeding the rest of the herd. Heifers take longer to cycle post calving than mature cows. By allowing a 3 week gap at breeding, first calf heifers will likely show heats post calving at the same time as the main herd. A breeding season of 45 days is adequate for heifers provided they are in good nutritional status. To maximise the return from heifers, it’s important to pregnancy check all heifers and cull those not in calf.
Heifers are very sensitive to calving difficulties. Research by Ontario Veterinary College has shown that on average 22% of first calf two year olds require assistance, and work by the University of Arkansas has shown that up 34% of first calf 2 year olds require assistance. Heifers must not be over or underfed as both conditions can lead to calving difficulties. The birth weight of the calf is related to genetics, less nutrition. Underfeeding will restrict the growth rate of heifers, reduce the size of the pelvis and increase the rate of calving difficulty. Overfeeding equally reduces the size of the birth canal due to excess fat deposition.
First calf heifers should be separated away from the main herd prior to calving. Calving should be monitored closely, but not obtrusively, to avoid increasing stress on the animal (which may delay calving), and provide assistance where necessary. The calving process tends to take longer in first calf heifers versus mature cows.
Always check that the newborn calf has sucked. First calf heifers are very inexperienced in allowing calves to suckle and assistance may be required. Great care must be taken when handling calves of heifers. A previously quite heifer may become extremely dangerous and unpredictable post calving.
The best method to reduce the risk of calving difficulties with first calf heifers is to breed heifers to an easy calving bull. Calving ease is the relationship between calf birthweight and cow pelvic size. Research has shown than in 80% of cases where calves die at birth, they were normal, and presented in the correct “diving” position, but the cause of death was suffocation. These types of deaths are primarily due to a mismatch between calf birth weight and dam pelvic size. Calf birthweight varies between breeds and within breeds, but a clear distinction exists between smaller framed, earlier maturing breeds and larger framed, later maturing breeds. Producers should select bulls with low calf birth weight when breeding heifers.
Pelvic measurements have been used by some producers as a means of selecting heifers for breeding. The University of Nebraska has developed ratios that can be used to determine the calf birthweight that a heifer could potentially successfully deliver. Measurements are taken at 12 to 13 months of age using a pelvimeter and from those measurements a maximum calf birthweight can be determined.
In Australia, pelvic measurements are primarily used as a culling tool to successfully identify abnormally small or abnormally shaped pelvises rather than as a breeding selection tool. These situations, if left unidentified, are associated with extreme calving difficulty, resulting in caesarean delivery and even death of the calf, cow or both.
Good selection and management of heifers for breeding is critical to the genetic advancement of the herd and the long term profitability of the beef farming enterprise.
References
Field, J. 2015, Feeding and Managing Replacement Beef Heifers, OMAFRA Fact Sheet.
Carson, Mark E., 2011, Preparing Heifers for Breeding, OMAFRA.
Lardner, Dr. Bart, 2014, Effect of Development System on Growth and Reproductive Performance of Beef Heifers. J. Anim. Sci. 7:3116-26.
Comerford, John W., 2011, Replacement Heifer Selection, PennState Extension.
Patterson, John, 2013, Tips to consider when selecting replacement heifers, Beef USA.
Patterson, David J., 1997, Pelvic Measurements and Calving Difficulty, University of Missouri Extension.
Troxel, Tom R., 2011, Pelvic Area Measurements in the Measurements of Replacement Heifers, University of Arkansas Agriculture and Natural Resources, FSA 3010.
Fahey, G., Boothby, D., Fordyce, G. and Sullivan, M. 2000, Female Selection in Beef Cattle, Queensland Beef Industry Institute, Q10047
Author: James Byrne, Beef Cattle Specialist, OMAFRA
