Effects of cow size on measures of efficiency in lactating multiparous crossbred beef cattle

Sixty multiparous cows (aged 5 to 6 years) of varying frame scores (FS; 5.17 ± 1.38) were used to examine relationships among body size (body weight [BW], FS, body volume [V]) and cow efficiency. Drymatter intake (DMI) and BW change were monitored during the 64-day experiment beginning one month prior to bull turnout. Cows were fed a forage-based diet with ad libitum access that was monitored using the Insentec feeding system. Average BW was collected (ABW; 1,459 ± 205.7 pounds) using the average of the two-day beginning and end BW. Measurements collected included body length, hip height, and heart, mid and flank girth. Measurements were collected at the beginning and end of the experiment, with measurements being used to calculate average V (166 ± 25.5 gallons). Calf BW was collected at the time of weaning. Positive correlation coefficients were found between DMI in pounds (lbs) and ABW, FS and V (P < 0.001; r = 0.84, 0.74, 0.81). The DMI (% of BW) tended to be negatively correlated with ABW and V (P = 0.08, 0.09; r = -0.24, -0.23). We observed positive correlation coefficients (P ≤ 0.05; r = 0.33, 0.28, 0.26) between WW (lbs) and negative correlation coefficients (P ≤ 0.05; r = -0.63, -0.57, -0.65) between WW (% of ABW) and ABW, FS and V. We saw a positive correlation coefficient (P = 0.04; r = 0.26) between calf ADG and ABW, and a tendency for a positive correlation coefficient (P = 0.09; r = 0.23) between calf ADG to weaning and FS. The observed correlation coefficients generally suggest that larger cows consume more pounds of feed and wean heavier calves with greater ADG to weaning, whereas smaller cows tend to consume more feed as a percentage of BW and wean a greater percentage of cow BW. Further research is needed on the complex relationship between cow size and efficiency.

In a cow-calf production setting, the calf is considered the output as opposed to the growth of the animal itself. As calves often are sold at weaning, achieving a high weaning weight (WW) comes with increased revenue. Costs that can be overlooked are those associated with the production of the calf, specifically feed intake of the dam, and this is often the largest cost within a cowcalf operation (Klosterman, 1972).

A common perception with cow-calf operations is that larger cows will wean larger calves, which has, in turn, led to larger cows being more favorable. While the perception is that larger cows are more efficient, some also have questioned if, when after all outputs and inputs are considered, smaller cows are in fact more efficient when weaning a calf and for profitability (Klosterman, 1972; Doye and Lalman, 2011).

This “argument” has resulted in increased interest in investigating the effect of cow size on efficiency. Determining the optimal type of cow to achieve maximum efficiency would provide producers with the ability to maximize profits.

Efficiency is a complex concept, with a general definition of the ratio of outputs to inputs. In cow-calf operations, common measures of efficiency include the WW of the calf compared with the size of the cow and/or the amount of feed consumed by the cow (National Academies of Sciences, Engineering, and Medicine [NASEM], 2016). The objective of this study was to examine the relationship of cow size and efficiency in a cow-calf operation through the measurement of feed intake of the cow and calf WW.

Sixty multiparous cows (1,459 ± 205.7 pounds; 5 to 6 years) accompanied with their calves were used in the experiment. Cows were housed at the NDSU Beef Cattle Research Complex (BCRC) for the duration of the experiment. Fifteen pairs were housed per pen, with four pens total and one separate calf pen per two pens where calves had access to grass hay.

Cows received a forage-based diet for ad libitum intake designed to meet estimated requirements (Table 1). Dry-matter intake (DMI) was monitored using the Insentec automated feeding system (Hokofarm group B.V., Marknesse, Netherlands). All cows had a predetermined body frame score, calculated based on hip height and age at weaning using BIF equations.

Cow body weight (BW) was taken on two consecutive days at the beginning and end of the experiment and on days one and two and days 63 and 64. Body measurements were collected at the beginning and end of the experiment. Calves were weighed upon arrival at the BCRC, twice in the middle of the experiment during a weigh suckle weigh procedure, and were weighed at the time of weaning (weaning weight).

Body size characteristics examined were average BW, body volume and frame score. Body volume was calculated using body measurements: body length, and heart, mid and flank girth, with the average of heart and flank girth representing the end girth.

Measures of efficiency included DMI as pounds and as a percent of cow BW, and calf WW as pounds and as a percent of cow BW. Phenotypic correlations between body size and measures of efficiency traits were determined using Proc MANOVA in SAS and correlations were spearman correlations.

Descriptive statistics for measures of efficiency traits are presented in Table 2 and correlation coefficients are presented in Table 3. Overall, larger cows consumed a greater amount of feed in pounds, compared with smaller cows (P < 0.001), while smaller cows consumed a greater percentage of BW of feed (P < 0.001). Smaller cows tended to wean a smaller calf, compared with larger cows (P = 0.06); however they weaned a larger percentage of BW (P = 0.05).

Measures of efficiency traits across all cows in the experiment include weight change (Wt change), average weight change per day (AVG Wt change/d), dry matter intake as lbs. (DMI) and as percent of body weight (DMI, % of BW), calf weaning weight in lbs. (Calf WW), calf weaning weight as a percent of cow body weight (Calf WW, % of BW) and calf average daily gain (Calf ADG).

Body size traits include average body weight (ABW), volume (VOL) and frame score (FS), and measures of efficiency include dry-matter intake (DMI), dry-matter intake as percent of body weight (DMIP), weaning weight (CWW), weaning weight as a percent of cow body weight (CWWP), calf average daily gain (CADG) and residual feed intake (RFI).

Three measurements were chosen to be included in a prediction equation (R2 = 0.75) for DMI: average BW (ABW), average weight change (AWC) and calf WW (CWW); DMI = 0.629 + 0.02(ABW) + 0.854 (AWC) + 0.015(CWW). A prediction model for DMI provides insight into what factors contribute to differences in DMI and potentially could be used to aid in making decisions relative to feeding and breeding management.

The authors thank U.S. Department of Agriculture National Institute of Food and Agriculture grant 2020-67016-31348 for funding and the staff at the Beef Cattle Research Complex and Dickinson Research Extension Center for their assistance with the project.

Doye, D., and Lalman, D.L. 2011. Moderate versus big cows: do big cows carry their weight on the ranch?

Klosterman, E.W. 1972. Beef cattle size for maximum efficiency. J. Anim. Sci.. 34: 975 - 880.

NASEM 2016. Nutrient requirements of beef cattle. 8th rev. ed. Washington, D.C.: National Academic Press.