How average daily gain is influenced by weather variables in beef steers

Average daily gain (ADG) is a measure of performance utilized by beef cattle producers. The objective of this study is to examine how weather variables influence ADG. This study utilized condensed intake data (13,739 steer-weeks observations) from 790 beef steers collected through an individual feeding system to evaluate how weather variables influence ADG. Ambient temperature, solar radiation, range of temperature, dew point and wind speed, as well as their two-week and monthly lag, were modeled while accounting for body weight (BW), dry matter intake (DMI), dietary energy density (NEm) and week of the year. The results from this study show that weather variables account for 55.4% additional variation in ADG. This indicates that weather variables affect ADG and should be included in models used for ADG

In beef cattle production, average daily gain is one of the most important measures used in assessing the productivity of finishing cattle. The amount of energy and other nutrients in the diet for beef cattle is the primary factor influencing growth of the animal (National Academies of Sciences, Engineering, and Medicine [NASEM], 2016). Factors such as genetics, environment, diet, mineral and vitamin supplements, feed additives, implants and ionophores all affect ADG, and expanded modeling of such terms is warranted.

A large component of the environment is weather because weather influences the physiology and thermal balance of an animal. The objective of this study was to evaluate the weather variables that influence ADG. This will improve the accuracy of the estimates utilized by producers in accounting for the quantity of energy required for growth and facilitate better productivity of the herd.

Individual intake data from 790 beef steers collected from 2011 to 2017 through an Insentec feeding system (RIC feeding system; Hokofarm Group, Marknesse, The Netherlands) were utilized for this study (n = 13,739 steer-weeks observations). Body weight, DMI, NEm and week of the year were standard fixed effects that were included (base model), additional variation accounted for by weather variables (ambient temperature, range of temperature, solar radiation, wind speed and dew point) then was evaluated.

For each weather variable, we modeled the direct week, two-week lag (average of the previous two weeks) or monthly lag (average of the previous month) independently. All data were condensed from daily to weekly averages to remove day-to-day variation. All modeling was done using the MIXED procedures of SAS (SAS Institute Inc., Cary, N.C.).

The descriptive statistics of the variables used in this study are shown in Table 1. The significant (P <0.05) main effects in our final model are shown in Table 2.

1 - SD = standard deviation, SE = Standard error

1 - DMI = dry matter intake, BW = body weight and NEm = dietary net energy of maintenance. Units are lb. for BW, lb./day for DMI, Mcal/lb. for NEm, F for ambient temperature, range of temperature, dew point and miles/hour for wind speed.

We observed a decrease in ADG with increasing solar radiation and increasing range of temperature (Figure 1a). Solar radiation has been reported to influence cattle by affecting physiology and thermal balance. This is why cattle with access to shade have been observed to perform better than unshaded cattle.

Figure 1: How ADG is influenced by the interaction between solar radiation and range of temperature (1a), dew point (1b), ambient temperature (1c) and wind speed.

In this study, at dew point temperatures below 27.5 F and increasing solar radiation, we observed an increase in ADG. On the other hand, with dew point temperatures above 43 F and increasing solar radiation, ADG decreased (Figure 1b). The radiant energy from the sun has been known to influence the thermal energy of the animal.

Cattle raised in the northern Great Plains experience long winters characterized by prolonged periods of cold. Solar radiation and temperature interacted to affect ADG. We observed an increase in ADG with increasing solar radiation and decreasing temperature (less than 21.7 F).

Average daily gain decreased with increasing temperature and increasing solar radiation (Figure 1c). This explains the impact of ambient temperature and solar radiation on the physiology of beef cattle and how they influence the thermal balance of cattle.

We observed a decrease in ADG with increasing solar radiation and increasing wind speed (Figure 1d). Wind has been reported to have an influence on the thermal environment. In cold environments, high winds make the temperature feel colder, which is generally regarded as wind chill.

The interaction between range of temperature and dew point and its effect on ADG is shown in Figure 2a. Average daily gain increases with increasing dew point and increasing range of temperature. On the other hand, ADG decreases with decreasing dew point and increasing range of temperature. This shows that the range of temperature (fluctuation) in temperature has an impact on the animal because cattle generally take time to fully acclimatize to changes in weather.

Figure 2: How ADG is influenced by the interaction between range of temperature and dew point (2a), and wind speed (2b).

The interaction between monthly lag of range of temperature and monthly lag of wind speed and its effect on ADG is shown in Figure 2b. As the range of temperature and wind speed increases, ADG decreases.

Dew point and two-week lag of ambient temperature interacted to affect ADG (Figure 3). At very low (minus 17 F) dew point and low temperature (minus 11 F), ADG is negatively influenced. As the temperature reached 37.9 F, dew point had a small effect on ADG. When the temperature was 70.5 F, a low dew point increased ADG but a high dew point decreased ADG.

Figure 3: How ADG is influenced by the interaction between dew point and ambient temperature.

No studies have examined the effect of weather variables on ADG of beef steers in the northern Great Plains. The results from this study
indicates that ADG is significantly influenced by weather variables and the addition of weather variables should be considered when making ADG predictions for improved accuracy.

National Academies of Science, Engineering, and Medicine. 2016. Nutrient requirements of beef cattle, 8th Rev. ed. Washington, D.C.: The National Academies.