Sward height is strongly related to the daily dry matter intake of grazing dairy cows, which consequently determines animal performance. Despite that, few studies have explored the potential to increase milk production by managing post-grazing sward height. An experiment was carried out to evaluate the effect of three defoliation intensities on a Lolium arundinaceum-based pasture on frequency and length of grazing meals and ruminating bouts, daily grazing and ruminating time, feeding stations and patches exploration, and dry matter intake and milk production of dairy cows. The treatments imposed were three different post-grazing sward heights: control (TC), medium (TM), and lax (TL), which were managed with 6, 9, and 12 cm of post-grazing sward heights during autumn and winter, and 9, 12, and 15 cm of post-grazing sward heights during spring, respectively. Thirty-six autumn-calving Holstein cows were grouped by parity (2.6 ± 0.8), body weight (618 ± 48) kg, and body condition score (2.8 ± 0.2) and randomized to the treatments. The pasture was accessed from 08:00 to 14:00 and 17:00 to 03:00 during spring and no supplement was involved during the evaluation period. Daily grazing time averaged 508 ± 15 min and was not affected by treatment. The reduction of post-grazing sward height increased the length of the first grazing session in the morning and the afternoon. The number of grazing sessions was greater on TL than on TM, with no difference in TC. The number of feeding stations (the hypothetical semi-circle in front of an animal from which the bites were taken without moving the front forefeet) visited was less on TC than on TL, and neither of them differed from TM. Dry matter (DM) intake was lesser on TC than on TM and TL (14.7 vs. 17.8 kg DM). Milk production during the evaluation period was 13.1, 16.2, and 18.7 kg/day for TC, TM, and TL, respectively. The milk fat, protein, and lactose content did not differ between treatments. The cows on TC exhibited a lower intake rate, although they were less selective, probably as a consequence of the sward structure of TC treatment. The cows on TM adopted a compensation mechanism which allowed them to achieve the same dry matter intake as cows on TL, but lower milk production. The cows on TL were more selective than TC and TM resulting in higher digestible dry matter intake and consequently higher milk production. The intensity of defoliation impacts on the animal-plant interaction, and constitutes a valuable management tool that can be used to boost forage intake and milk production. The new developments on information technology would allow researchers to link behavioral data with response variables (e.g., milk production, health, welfare, etc.) at different spatio-temporal scales and support short and long-term management decisions.

The objective of the present study was to perform a meta-analysis that compared the chemical composition of corn silage produced for different experimental purposes, i.e., by research groups that studied corn silage (SCS) or by research groups that only used corn silage (UCS) as a form of roughage. We analyzed 203 papers that were published between January 1994 and December 2014 and contained a total of 647 treatments and the analysis of 1701 silos. We found a significant difference (P < 0.0001) in the dry matter (DM) content of SCS silage (33.00%) and that of UCS silage (30.64%). The DM contents of neutral detergent fiber for the SCS and UCS silage were high (54.72 and 55.14% DM, respectively) but were not significantly different from one another (P = 0.5936), and the acid detergent fiber content of the UCS silage (31.04% DM) was higher than that of the SCS silage (29.65%, P = 0.0214), which indicated that the UCS silage was less digestible than the SCS silage. This was also corroborated (P = 0.0064) by the mean content of total digestible nutrients (64.18% DM) in the UCS silage, which likely results from the lower level of care taken when using standard silage production methods, compared to that taken by SCS researchers. Therefore, we concluded that the corn silage produced by research groups in Brazil are not analyzed in full and that, as a result, there is a paucity of important information, such as the content of organic acids. In addition, we also found that corn silage produced in Brazil contains a high level of neutral detergent fiber.

Dairy cows' productive performance is influenced by various factors, including nutrition, housing comfort, and weather conditions during grazing. In classic confinement systems, animal comfort is typically ensured through ventilation and sprinkling features. However, in mixed feeding systems, controlling environmental conditions at the supplementation site is less common. The present 2-yr study evaluated 2 lactations and 2 calving seasons (autumn and spring) with 3 treatments that combined 2 housing systems (compost barn [CB] or outdoor soil-bedded pens with shade structures [OD]) and 2 feeding strategies with varying proportions of grazing (TMR with no grazing and one-session grazing supplemented with mixed ration [GRZ]). The treatments resulted in the following combinations: (1) CB-confined cows fed a TMR ad libitum (CB-TMR); (2) CB housing with GRZ (CB-GRZ); and (3) OD housing with GRZ (OD-GRZ). Data collected included milk production and composition, feed intake, BCS, BW, and cyclicity. The confined system resulted in higher milk and milk solids production per cow than the mixed feeding systems, with differences being more pronounced in the spring- than in the autumn-calved cows. However, contrary to our hypotheses, the differing environmental exposure in the 2 mixed feeding systems did not affect overall performance, although under certain exposure conditions, the CB outperformed and better protected against heat stress than the OD during several weeks of the trial. In OD-GRZ, milk solids production per cow was greater in autumn- than in spring-calving season, whereas solids production in CB-TMR and CB-GRZ did not differ between autumn- and spring-calving cows. Total DMI and feed efficiency, as well as the amount of concentrate per unit of milk, were higher for the confined system than the mixed feeding systems, with no effect of calving season or environmental exposure level between the 2 mixed feeding systems. Confined cows maintained higher body reserves throughout the trial, with no effects of environmental exposure in the mixed feeding systems. The OD-GRZ had the highest operating profit and return on assets, followed by CB-GRZ and CB-TMR. In conclusion, in the mixed feeding system, performance was not affected by housing conditions at the supplementation site, whereas profitability was higher for OD-GRZ. Regardless of calving season, confined cows produced more milk than mixed feeding cows, with differences being more pronounced in spring-calving compared with autumn-calving cows.

Grazing dairy production systems have gained interest due to the increasing consumer preferences associated with environmental care and animal welfare perception. Nonetheless, grazing dairy cows have lower feed conversion than those fed indoors with a TMR, partly because of increased maintenance energy costs associated with grazing and walking activity. However, to our knowledge, the energy cost of grazing has not been quantified for dairy cows. The objectives of the present work were to evaluate the effects of grazing on the oxygen pulse (O₂P; mL O₂ consumed per heartbeat; experiment 1) and to quantify the energy cost of grazing in dairy cows using the oxygen pulse-heart rate (O₂P-HR) technique (experiments 1 and 2). In both experiments, heat production (HP) was measured using the O₂P-HR technique and synchronized with animal activity records. In experiment 1, 15 dairy cows were used to measure the O₂P when resting and then immediately after the first grazing session to assess the effect of grazing on O₂P. Grazing activity increased HR and oxygen consumption compared with when the cows were resting. However, the increase in both variables was proportional; therefore, O₂P was similar, indicating that the change in HR was the main component in the response to an increased O₂ demand due to grazing. Hence, it is possible to use the O₂P-HR method to measure HP during grazing in dairy cows. The energy cost of grazing was estimated by the difference in HP between when the cow was grazing and when it was not grazing (i.e., idling or ruminating) and ranged from 6.63 ± 1.12 to 7.85 ± 0.68 kJ/kg^0.75 per hour and 1.31 ± 0.28 to 1.59 ± 0.14 kJ/kg per hour, respectively. In addition, the energy cost of walking was calculated as the difference in HP when the cow was walking to and from the pasture and the milking parlor versus when it was idling or ruminating. The energy cost of walking was 24.03 ± 1.12 kJ/kg^0.75 per hour or 4.72 ± 0.28 kJ/kg per hour. Hourly energy expenditure (kJ/h) was similar between grazing and consuming TMR at the feed bunk, indicating that the extra energy required by dairy cows when fed in a grazing system is mostly explained by the longer time spent to harvest the pasture and the energy cost of walking between the pasture and the milking parlor compared with confined cows fed TMR. Finally, the results of this study suggest that O₂P is not affected by grazing and therefore that the O₂P-HR technique is a promising methodology to estimate the energy cost of grazing animals without substantially affecting their behavior within the production system.

Residual sward height management is a key factor influencing milk production and grazed forage utilization per cow and per hectare in pasture-based dairy systems. This study evaluated the effects of postgrazing sward height on forage growth rate and DMI, milk production, and BCS in supplemented, high-producing dairy cows. The study captured cumulative treatment effects on animal performance across nearly an entire lactation, as well as sward dynamics over most of the tall fescue growing season. Thirty-two multiparous Holstein cows were assigned to 2 treatments: the control treatment, with a postgrazing sward height of 5.0 to 7.0 cm (CT), and the high treatment, with a postgrazing sward height of 12.0 to 15.0 cm (HI). The study spanned 215 d of grazing on a Lolium arundinaceum sward in a randomized complete block design, with 4 blocks, each measuring 3.2 ha, and consisted of 2 paddocks, each measuring 1.6 ha. Cows had one grazing session between milkings and were supplemented with a mixed ration in the opposite session. Rotational grazing was employed, with new strips allocated once the postgrazing sward height for each treatment was achieved. A new grazing cycle was initiated when plants reached the 2.5 to 3.0-leaf phenological state. Any extra or unused areas within a grazing cycle were always recorded. The postgrazing sward heights were 7.7 and 14.4 cm for the CT and HI treatment, respectively. Forage growth rate tended to be 21% higher in the HI treatment (40 vs. 33 kg DM/ha per day), and cows stayed longer per strip (3.9 vs. 2.9 d) and had 2.5 times more grazing cycles (8.3 vs. 3.3). Total forage disappearance was similar between treatments. Cows in the HI treatment had greater individual grazed forage DMI (+2.0 kg/cow) and BCS throughout lactation compared with CT cows. The HI treatment also increased the individual milk production by 10% (31.5 vs. 34.5 kg milk/d) while reducing concentrate intake per unit of milk by 10%, resulting in a tendency for higher income over feed costs at cow level. However, although we observed a tendency for a higher forage growth rate, this approach required a larger grazing area (1.18 vs. 1.60 ha/4 cows), leading to a trend toward 21% lower milk output per hectare (23,598 vs. 18,528 kg milk/ha). In contrast, the CT treatment supported a higher stocking rate but resulted in lower grazed forage DMI, higher supplemental feed input per hectare and slower BCS recovery. These findings highlight the importance of aligning grazing strategies with system-specific goals. Farmers seeking to maximize land productivity may favor lower postgrazing sward heights, although these must be managed carefully to prevent adverse effects on animal health, reproduction, and long-term productivity due to slower BCS recovery during lactation and lower BCS at the onset of dry off. Conversely, systems aiming to reduce feed costs may benefit from a higher residual sward height, which enhances individual cow performance and BCS while decreasing reliance on supplemental feed.