Stabilizing Total Mixed Ration Dry Matter to Mitigate Environmental-Relative-Humidity Effects on Lactating Cow Performance

Abstract

This study evaluated environmental relative humidity's (ERH) impact on dry matter (DM) in hay and total mixed ration (TMR), exploring strategies to stabilize milk production in lactating cows by maintaining a consistent TMR DM content. We hypothesized that precise TMR DM adjustments mitigate ERH effects on milk production stability. Experiment 1 showed that grass hay exhibited greater DM variability than alfalfa hay under high ERH. Experiment 2 revealed that high daily ERH variability (>25%) caused fluctuations in hay moisture, affecting TMR DM stability. Increasing TMR DM reduced milk composition variation. In Experiment 3, precise TMR DM adjustments and heat stress levels were evaluated under different temperature-humidity indexes (THIs) in 46 cows over three 28-day periods. The results showed a significant improvement in milk yield (non-adjustment: 26.99 vs. adjustment: 27.29; SEM: 0.32; THIs: 65 to 82; p < 0.05) and a reduction in the variation in milk composition under heat stress. The differences in energy-corrected milk were lower (non-adjustment: 0.47 ± 0.06 vs. adjustment: 0.20 ± 0.09; p < 0.05). This study confirmed that monitoring hay DM and adjusting TMR DM stabilize milk production under variable ERH. Dairy producers can implement routine hay DM monitoring and TMR adjustments to enhance lactating cows' performance.

Keywords: dry matter; energy-corrected milk; hay; moisture stabilization; precision feeding; temperature–humidity indexes.

Figure 1

Association between (a) alfalfa (red line) and (b) grass hay (blue line, 1:1 mixture of oat hay and Timothy hay) moisture contents (%) and environmental relative humidity (ERH) differences (%) within a day (each dot represents the average of 10 bale samples). The hay moisture content was analyzed using the PROC MIXED procedure for repeated measures. The associations between ERH and hay moisture content were analyzed using regression analysis within the MIXED procedure of SAS 9.4. Treatment comparisons were performed using the Tukey adjustment for multiple comparisons. p values > 0.05 and ≤0.10 were considered to indicate a trend, whereas p values < 0.05 were considered to indicate significance.

Figure 2

Association between total mixed ration (TMR) dry matter (DM, %) and ERH difference (%) within a day in high- and low-yield groups under environmental relative humidity (ERH) > 75% or <75%. The top figure displays data under ERH > 75% (red lines). The bottom figure displays data under ERH < 75% (blue lines). The data for the high- and low-yield groups were obtained from 84 TMR samples across all treatment groups (each dot represents the average of TMR samples).

Figure 3

Association between total mixed ration (TMR) dry matter (DM, %) and ERH difference (%) within a day in high- and low-yield groups for environmental relative humidity (ERH) difference > 25% or <25%. The top figure shows the association when the ERH difference was >25% (red lines). The bottom figure shows the association when the ERH difference was <25% (blue lines). The data for the high- and low-yield groups were obtained from 84 TMR samples across all treatment groups (each dot represents the average of TMR samples).

Figure 4

Association between milk production (kg/d) and total mixed ration (TMR) dry matter (DM, %) as well as association between the coefficient of variation (CV, %) of milk production (kg/d, black lines), fat (%, red lines), total solids (%, purple lines), and protein (%, blue lines) and TMR DM (%) in the high-yield group (each dot represents the average milk production and composition in CV% of experimental cows). (a) Data for cows producing 30–40 kg/d and (b) data for cows producing > 40 kg/d.

Figure 4

Association between milk production (kg/d) and total mixed ration (TMR) dry matter (DM, %) as well as association between the coefficient of variation (CV, %) of milk production (kg/d, black lines), fat (%, red lines), total solids (%, purple lines), and protein (%, blue lines) and TMR DM (%) in the high-yield group (each dot represents the average milk production and composition in CV% of experimental cows). (a) Data for cows producing 30–40 kg/d and (b) data for cows producing > 40 kg/d.

Figure 5

Association between milk production (kg/d) and total mixed ration (TMR) dry matter (DM, %), as well as association between the coefficient of variation (CV, %) of milk production (kg/d, black lines), fat (%, red lines), total solids (%, purple lines), and proteins (%, blue lines) and TMR DM (%) in the low-yield group (each dot represents the average milk production and composition in CV% of experimental cows). (a) Data for cows producing 20–30 kg/d and (b) data for cows producing < 20 kg/d.

Figure 5

Association between milk production (kg/d) and total mixed ration (TMR) dry matter (DM, %), as well as association between the coefficient of variation (CV, %) of milk production (kg/d, black lines), fat (%, red lines), total solids (%, purple lines), and proteins (%, blue lines) and TMR DM (%) in the low-yield group (each dot represents the average milk production and composition in CV% of experimental cows). (a) Data for cows producing 20–30 kg/d and (b) data for cows producing < 20 kg/d.

Figure 6

Effect of the temperature–humidity index (THI) and total mixed ration (TMR) dry matter (DM) adjustment on milk production during the experimental period (Experiment 3). (a) Cows with days in milk (DIM) less than 90; (b) cows with DIM between 90 and 150. NA: non-adjusted; Adj: adjusted.