The objective of this study was to determine the effect of reducing the particle size of wheat straw in a total mixed ration (TMR) on cow behavior, health, and production in early lactation. For 28 d after calving, 41 multiparous Holstein cows were individually provided either 1 of 2 TMR with 9% wheat straw (dry matter basis) chopped (1) using a 2.54-cm screen (short; n = 21) or (2) using a 5.08-cm screen (long; n = 20). Cows were housed in freestall pens during both the dry and lactating period. Enrollment in the trial was on a rolling basis and cows were evenly distributed by parity and milk production between treatments. Wireless telemetry boluses were used to measure reticulorumen pH. Automated systems recorded TMR dry matter intake, milk yield, and rumination activity. The TMR and orts samples were collected every 3 d to determine feed sorting. A particle separator was used to separate feed samples into 4 fractions: long (>19 mm), medium (<19 mm, >8 mm), short (<8 mm, >4 mm), and fine (<4 mm) particles. Feed sorting was calculated as actual intake of each particle fraction expressed as a percentage of its predicted intake. Cows sorted the longest TMR particles differently by treatment; on the long treatment cows sorted against long particles (94.2 ± 1.9%), whereas on the short treatment cows did not sort for or against these particles (99.7 ± 1.9%). Data were analyzed in mixed-effect linear regression models and fitted with polynomial functions over the 28 d of observations. The fitted data indicated treatment differences in linear coefficients, quadratic coefficients, and cubic coefficients for mean time (min/d) below a reticulorumen pH of 5.8 and milk yield. Rumination time (min/d) differed between treatments for quadratic and cubic coefficients. Cows on the short treatment linearly increased in dry matter intake at a greater rate than cows on the long treatment. Mean reticulorumen pH decreased at a greater rate for cows on the long treatment than for cows on the short, as indicated by differences between linear coefficients. Cows on the short treatment tended to produce 75 kg more milk cumulatively during the first 28 d in milk than cows on long treatment. These results suggest that cows fed a diet with longer straw particles selected against physically effective fiber, which may have contributed to greater fluctuations in rumination time, reticulorumen pH, dry matter intake, and milk production in early lactation.

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Beef cattle are commonly fed a high-concentrate, grain-based diet in the finishing period. Longer forage particles stimulate chewing and rumination, which may increase saliva production to buffer the rumen, mitigating a harmful drop in pH that can result from a high grain diet. Our objective was to quantify motivation of finishing cattle to access forage with a short-term thwarting test. We predicted cattle would show more interest in forage, versus an additional offering of their primary diet, during initial exposure and when access to this resource was thwarted. Sixteen finishing cattle were fed a high-concentrate primary diet (16% forage) ad-libitum. Twice per day for 4 days, cattle were exposed to 1 of 2 treatments for a maximum of 1 hr/exposure: 1) 100 g of beardless wheat hay (WH; n=7) or 2) 100 g of the primary diet (TMR; n=9). On the 5th day, the bins containing the dietary treatments were covered with a metal mesh that thwarted access to the contents while still allowing visual and olfactory contact. Interaction with and time spent in proximity to the bins were video recorded and feed intake recorded during days 1–4. T-tests did not detect treatment differences during the thwarting test in any behavioral response (p≥0.292). However, repeated measures analysis indicated that intake of the dietary treatments and interactions with the bin decreased over days 1–4 for WH cattle, while these same measures increased for TMR cattle (day*treatment, p≤0.001). These results suggest that animals were more interested in eating and interacting with additional high-concentrate diet than with a small amount of forage. Our findings may be explained by several factors, including that the TMR was highly palatable or that the inclusion rate of forage in the primary diet may have been sufficient, thus cattle showed little motivation for forage during the thwarting test.

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