Production calculations related to beef cow nutrition

News
May 31, 2013
by WLJ

Calving distribution, the number of cows calving in 21-day periods during the calving season, is impacted by the nutrition program and therefore body condition at calving, especially for spring-calving cows. Cows that cycle early in the breeding season conceive early in the breeding season, and calve early in the calving season.

Twenty-one day calving intervals can be easily calculated if you know when to start the first 21-day interval. Standard Production Analysis Guidelines indicates there are two ways to determine when to start the first 21-day calving interval.

Start when the third mature cow (3 years old or older) has calved—OR— start the first 21-day calving period 285 days after the start of the breeding season.

Sixty-five percent or more of the cows should calve in the first 21-day calving period. Calving distribution can be influenced easily by monitoring body condition/ nutrition prior to calving. Cows that calve in adequate body condition (BCS = 5) tend to breed earlier in the breeding season and calve earlier in the calving season. Calves from these early-calving cows are older and heavier at weaning compared to calves from cows that breed later in the breeding season.

Many times a minor change in nutrition management before calving results in cows breeding ear lier.

This can have a substantial impact on weaning weight of those early-conceived calves as early-born calves weigh more than later-born calves when weaned on the same date.

Calf Crop Percentage

Calf Crop Percentage may be the most important production calculation that a cow/calf producer can record. The reason for this statement is that Calf Crop Percentage has both an input and output component.

Inputs include nutrition and management, management during the breeding season, management during the calving season, and management from calving to weaning. The output component is reproduction, and reproduction impacts pounds of weight that is available to sell at weaning.

Following is an abbreviated method to dissect performance of your cow herd by stage of production:

Percentage calves weaned of females exposed is the number of calves weaned based on the females that were exposed to the bulls to produce the calves that are being weaned. Mathematically, it is the number of calves weaned (numerator) divided by the number of females exposed to produce that calf crop (denominator) and this number times 100 to make it a percentage [(# calves weaned/# cows exposed) x 100].

The challenge sometimes is that the numbers needed to do the calculation are collected over a year apart. For females that wean a calf in October of 2013, the number of females exposed would be the number of females exposed to a bull during the breeding season in 2012.

This process can be used to dissect percent weaned of exposed into different phases of the production cycle to get at pregnancy percent, calving percent, and weaning percent.

Pregnancy Percent is the number of pregnant females divided by the number of females exposed to the bulls during the breeding season.

Calving Percent is the number of females that calve divided by the number of pregnant females.

Weaning Percentage is the number of calves weaned divided by the number of live calves that were born and nursed their dam.

Using the preceding definitions would produce these indicators.

Pregnancy Percent gives an indicator of number of non-pregnant females.

Calving Percent gives an indicator of abortions after pregnancy testing as well as calves lost at calving due to dystocia.

Weaning Percent gives an indicator of calf losses from calving to weaning.

As an example, in a 300-head cow herd, 255 cows weaned a calf. Records indicate 37 cows with no calving records, 6 calves lost at calving, and 2 calves lost between calving and weaning. We assumed the 37 head were non-pregnant because there was no record that they aborted.

Pregnancy percentage is 87.7 percent = ([(300 - 37)/300) x 100] = (263/300) x 100)]

Calving percentage is 97.7 percent = [(263 - 6)/263) x 100) = (257/263) x 100]

Weaning percent is 99.2 percent = [(257 - 2)/257) x 100 = (255/263) x 100].

If you multiply pregnancy percent x calving percent x weaning percent, the result should be close to 85 percent. This value is the Calf Crop Percentage.

Calf Crop Percentage= 84.99 percent or 85 percent = (.877 x .977 x .992) x 100.

A producer can further dissect cow reproductive performance by age group using the process described above. If a large number of young spring-calving females are not pregnant with their second calf, it is likely due to the lack of energy in their diet after calving.

There are Standardized Performance Analysis (SPA) guidelines that outline how to calculate production measures for the cow herd and how to account for pregnant females and cow/calf pairs entering and exiting the herd. SPA guidelines can be found on the National Cattlemen’s Beef Association website or ask your state beef cow specialist to help you locate the SPA production guidelines. — Rick Rasb, Beef Specialist, University of Nebraska

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