Predicting feed intake in confined beef cows

Authors: GROSS, MEGAN - Oklahoma State University; HOLDER, AMANDA - Oklahoma State University; MOEHLENPAH, ALEXI - Oklahoma State University; FREETLY, HARVEY - Retired ARS Employee; GOAD, CARLA - Oklahoma State University; BECK, PAUL - Oklahoma State University; DEVUYST, ERIC - Oklahoma State University; LALMAN, DAVID - Oklahoma State University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2024
Publication Date: 1/4/2024
Citation: Gross, M.A., Holder, A.L., Moehlenpah, A.N., Freetly, H.C., Goad, C.L., Beck, P.A., DeVuyst, E.A., Lalman, D.L. 2024. Predicting feed intake in confined beef cows. Translational Animal Science. 8. Article txae001. https://doi.org/10.1093/tas/txae001.
DOI: https://doi.org/10.1093/tas/txae001

Interpretive Summary: An accurate estimate of feed intake is a fundamental component necessary to determine nutrient balance and project animal performance. Three feed intake equations for nonlactating beef cows and three feed intake equations for lactating beef cows were evaluated. These equations were developed primarily from data published between 1979 and 1993. The validation data set was restricted to projects conducted or published since 2002. An independent data set was used to evaluate equations available to estimate feed intake in beef cows. One equation (Hibberd and Thrift, 1992) provided a reasonably accurate estimate of feed intake for lactating cows, although the equation from the same authors overestimated feed intake in nonlactating cows. A new model was developed that included stage of production, body weight, and diet energy concentration. None of the three equations evaluated provided an accurate estimate of feed intake for nonlactating cows. Most of the error associated with The National Research Council (1996) equation was from unexplained error in nonlactating cows and from prediction bias in lactating cows due to underestimation of feed intake. The new equation accounted for 68% of the variation in daily feed intake. Diet energy concentration, body weight, and stage of production, accounted for 41.6, 12.5, and 8.0% of the variation in feed intake, respectively. The next step is to validate the new proposed equation with an independent data set.

Technical Abstract: Six existing equations (three for nonlactating and three for lactating; NRC, 1987, Predicting feed intake of food-producing animals. Washington, DC: The National Academies Press, National Academy of Science; doi: 10.17226/950; NRC, 1996, Nutrient requirements of beef cattle, 7th Revised Edition: Update 1996. Washington, D: The National Academies Press; doi: 10.17226/9791; Hibberd and Thrift, 1992. Supplementation of forage-based diets. J. Anim. Sci. 70:181. [Abstr]) were evaluated for predicting feed intake in beef cows. Each of the previously published equations are sensitive to cow shrunk BW and feed energy concentration. Adjustments in feed intake prediction are provided for level of milk yield in the NRC (1987. Predicting feed intake of food-producing animals. Washington, DC: The National Academies Press, National Academy of Science; doi: 10.17226/950) and NRC (1996 Nutrient requirements of beef cattle, 7th Revised Edition: Update 1996. Washington, DC: The National Academies Press; doi: 10.17226/9791) equations. The equation published in 1996 used data generated between 1979 and 1993. Our objectives were to validate the accuracy of the published equations using more recent data and to propose alternative prediction models. Criteria for inclusion in the evaluation data set included projects conducted or published since 2002, direct measurement of feed intake, adequate protein supply, and pen feeding (no metabolism crate data). After removing outliers, the data set included 53 treatment means for nonlactating cows and 32 treatment means for lactating cows. Means for the nonlactating data set were DMI = 13.2 ± 2.9 kg/d, shrunk body weight (SBW) = 578 ± 83.9 kg, body condition score = 5.7 ± 0.73, and Mcal net energy for maintenance (NEm)/kg of feed = 1.27 ± 0.15 Mcal/kg. Means for the lactating dataset were DMI = 14.6 ± 2.24 kg/d, SBW = 503 ± 73.4 kg, body condition score = 4.7 ± 0.58, and Mcal NEm/kg feed = 1.22 ± 0.16. Simple linear regression was used to determine slope, intercept and bias when observed DMI (y) was regressed against predicted DMI (x). The NRC (1996. Nutrient requirements of beef cattle, 7th Revised Edition: Update 1996. Washington, DC: The National Academies Press; doi: 10.17226/9791) nonlactating equation underestimated feed intake in diets moderate to high in energy density with intercept differing from 0 and slope differing from one (P =/< 0.01). Average deviation from observed values was 2.4 kg/d. Similarly, when the NRC (1996. Nutrient requirements of beef cattle, 7th Revised Edition: Update 1996. Washington, DC: The National Academies Press; doi: 10.17226/9791) equation was used to predict DMI in lactating cows, the slope differed from one (P < 0.01) with average deviation from observed values of 3.0 kg/d. New models were developed by pooling the two data sets and including a categorical variable for stage of production (0 = nonlactating and 1 = lactating). Continuous variables included study-average SBW0.75 and diet NEm, Mcal/kg. The best-fit empirical model accounted for 68% of the variation in daily feed intake with standard error of the estimate Sy root mean squared error = 1.31. The proposed equation needs to be validated with independent data.