Bull's Eye Consulting

10/10/2026

Weaning weight (3): Wean index calculation
The wean index of a calf is a calculation used to easily evaluate a calf's growth performance within its contemporary group. It is calculated by dividing the calf’s growth rate (average daily gain per day of age or ADA), after its weight was adjusted for age and the age of its dam, by the average 205-day ADA of the group (contemporaries) of calves, given as a percentage. A wean index of 110 thus means that the calf’s growth rate was 10% higher than the group's average. Please note that the wean index is an evaluation of both a cow’s milk production and the calf’s growth rate up to weaning.

08/10/2026

02/10/2026

Weaning weight (2): Comparing calves:
A basic principle in comparing the weights of a group of calves is to ensure that you compare apples with apples, i.e. to compare only calves that are comparable. The growth performance of a calf is usually assessed by comparing the calf’s growth rate per day at weaning to the average of its contemporaries. A contemporary group is a group of animals born in the same year, in the same season (similar age range), at the same location (same farm and herd), of the same s*x, rearing status, and managed alike (same feeding, treatments, etc.) from birth to the time of weaning.

To enable fair comparisons within a contemporary group, the following should be done:
• Only calves of the same s*x should be compared or, if they are compared across s*x, their weights should be adjusted for the effect of s*x.
• Weaning weights should be adjusted for the age of the mother to a mature cow basis.
• Only calves born within a certain period (e.g. 100 days) should be compared and their age should also be within certain limits (e.g. 150 – 270 days of age). Within such a group, the actual weaning weights should be adjusted to a constant age (e.g. 205-days) to enable fair comparisons.

Given that the contemporary grouping and weight and age of mother adjustments were properly done, the remainder of the variation in weaning weights within a contemporary group will reflect the genetic variation between animals.

25/09/2026

Weaning weight (1): Factors affecting weaning weight

The following are the most important factors affecting a calf’s weaning weight:

Maternal factors:
• Age of dam: In general, calves of mature cows (about 5-10 years of age) are heavier than calves from young cows and, to a lesser degree, old cows.
• Milk yield: The genetic merit of the dam for maternal ability (milk production, caring for the calf, etc.). A cow’s daily milk production has a very large effect on the calf’s weaning weight.
• Cow body condition and weight: Heavier cows and those with better body condition scores at calving or during lactation wean heavier calves because they provide more milk and better maternal care. The reproduction and production history of the cow, e.g. a cow that didn’t calve the previous year or who didn’t raise a calf the previous year, could have an influence on her calf’s weaning weight because the cow could accumulate additional reserves.

Calf factors:
• S*x of calf: Male calves are on average about 8% heavier than heifer calves at weaning.
• Age of calf at weaning: Older calves will in general be heavier than younger calves.
• Birth Weight: Calves with higher birth weights tend to grow faster and have heavier weaning weights, though extremely high birth weights can cause calving difficulties.
• Rearing status of the calf: Twin calves are typically about 10% to 17% lower in individual weaning weight compared to singletons.

Environmental and management factors:
• Nutrition and pasture quality: The quality and availability of natural grazing, forage, and supplementary lick/creep feed directly dictate pre-weaning growth rates.
• Season and year of birth: Annual rainfall, droughts, and seasonal temperature shifts change pasture conditions and forage availability, leading to distinct weight differences across seasons and years.
• Health and parasites: Calves that suffer from sickness, ticks, or worms require more energy to fight disease, which lowers their daily weight gain.

Genetic factors:
• Heterosis (hybrid vigour) from crossbreeding significantly improves pre-weaning growth and boosts the weaning weight of the calf compared to purebred averages.
• Direct and maternal heritability: Genes inherited directly from the sire and dam for growth rate (direct effects), as well as genes controlling the mother's milking and nursing ability (maternal effects), determine weaning weight.

12/09/2026

Birth weight (3): Environmental factors affecting birth weight
Maternal body weight or size:
Birth weight, as a percentage of dam weight, averages approximately 7% in cattle. Lighter body weight breeds tend to produce calves of lower relative birth weights compared to heavier body weight breeds.
Dam age:
Birth weights gradually increase with dam age until 5 or 6 years of age, and decline once the cow reaches 9 to 11 years of age.
Maternal ability:
Birth weight is affected by the dam’s maternal ability, defined as the dam's physiological capacity to nurture the developing foetus.
Foetal number:
The birth weight of twin calves is on average 10 to 30% lighter than that of single calves. The combined birth weight of twin calves represents approximately 12% of the dam's weight.
Gestation length:
Generally, a longer gestation period allows for additional foetal growth and results in a higher birth weight. The foetal growth rate near-term varies between 100 and 250 g per day.
Dam nutrition:
Feeding excessive energy during the last half to one-third of gestation can profoundly increase birth weight. Generally, energy intake during pregnancy influences birth weight more than protein intake.
Environmental temperature:
Birth weight depressions can be as much as 35% in ill-adapted animals chronically exposed to elevated environmental temperatures.
Season:
Birth weight effects due to season are usually variable and inconsistent and might be the result of differences in environmental temperatures as well as nutrition.

22/08/2026

Birth weight (2): Genetic factors affecting birth weight
Although factors affecting birth weight can be grouped, for convenience, into genetic and environmental causes, this is obviously an artificial division that might be misleading. The observed differences are often the result of an interaction between the environment and the genotype.
GENETIC EFFECTS
Sire and dam:
Heritability estimates for birth weight (direct) range from 0.1 to 0.45. The effect of sire on birth weight is therefore profound and includes genetic differences between sires within a breed and even between breeds.
Breed:
Birth weight differences among purebred cattle breeds reflect the combined genetic effects of sire and dam and are relatively dramatic, generally being greater than differences observed within breeds.
Heterosis:
Heterosis can profoundly influence birth weight in cattle depending upon the breed or breed type utilised. Whereas the effects between standard British or European beef breeds can range between 0 and 5%, these effects can be as high as 20% when Bos ta**us breeds are crossed with Bos indicus.
Inbreeding:
Inbreeding usually results in lower birth weights. Greater weight depressions are observed in calves that are in**ed, compared to calves from dams that are in**ed.
S*x of calf:
Male calves are approximately 5% to 8% heavier than female calves. Male calves are also associated with longer gestation lengths.
Genetic anomaly and malformation:
Birth weight might be affected by numerous genetic malformations. These conditions are usually the result of congenital defects in cattle.

13/08/2026

Birth weight (1): The importance of birth weight
Birth weight of calves is of critical importance for efficient beef production.
Calves that are too small may lack vigour, tolerance to cold stress, resistance to pathogens, and the ability to overcome parturition-related stresses.
Calves that are too large may cause varying degrees of dystocia, leading to increased calving problems, metabolic and respiratory acidosis, depressed immunoglobulin absorption, and increased susceptibility to disease. Calves that are too large also cause dams to take longer to conceive, leading to longer calving intervals and ultimately lower reproduction rates.

05/08/2026

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11/07/2026

Inbreeding (4) - Prepotency
Inbreeding promotes an increase in prepotency, which is the ability of a sire or dam to consistently pass on its characteristics. Prepotency results from an increase in homozygosity. Since an in**ed animal will have more homozygous gene pairs than a non-in**ed animal, there are fewer possible gene combinations for the s***m or egg cells. As a result, the offspring should be more similar to each other. However, the advantage of prepotency is more than counteracted by the decline in selection intensity and the loss of genetic variation due to inbreeding.

04/07/2026

Inteling (3) - Inteelkoëffisiënt
Inteling word gemeet deur middel van die inteelkoëffisiënt. Die inteelkoëffisiënt meet die persentasie toename in die homosigotiese gene pare in 'n individu relatief tot die gemiddelde van die populasie waaruit die individu kom. Indien 'n dier 'n inteelkoëffisiënt van 0.25 het, word dit verwag dat daardie dier 25% meer homosigotiese genepare sal hê as 'n nie-ingeteelde dier van dieselfde populasie. Die inteelkoëffisiënt kan enige waarde hê tussen 0 (0% ingeteel) en 1 (100% ingeteel). 'n Volbroer-suster paring sal lei tot 'n inteelkoëffisiënt van 25% in die nageslag; 'n vader-dogter paring ook 25%; 'n halfbroer-suster paring 12.5%; ’n ouma-kleinseun paring ook 12.5% en ’n neef-niggie (gemeenskaplike grootouers) paring 6.25% (in alle gevalle met die aanname dat die ouers nie self ingeteel is nie).