Milk yield and composition and body weight of offsprings of mixed-breed goats on semi-arid rangelands with different rainfall.

The objective was to characterize milk yield and composition from mixed-breed goats kidding in winter and grazing rangelands with 221 (n = 15), 334 (n = 20), or 441 (n = 12) mm of annual rainfall in northern Mexico (22-25°N). Weekly milk yield and composition were recorded and progeny growth performance assessed. Body weight loss during lactation was the highest (6.4 kg) for goats on rangeland with 441 mm of rainfall than goats on 221 mm (1.6 kg), or 334 mm (1.8 kg; P < 0.01). The highest daily milk yield was for goats on 221 mm (498 mL; P < 0.01). There was not an evident peak of lactation and milk yield increased uninterruptedly at the end of lactation. Milk fat was negatively related to milk yield and goats on rangeland with 334 mm had the greatest milk fat content (P < 0.001). Milk protein and lactose content were higher in goats on rangeland with 221 mm (P < 0.01). Goat kids on rangelands with 221 and 441 mm grew faster and were heavier (P < 0.001) at weaning than kids reared in other rangelands. Weaning weight was positively related to milk yield (P < 0.001); but not milk components (P > 0.05). In conclusion, moderate milk yield of mixed-breed goats on rangeland is feasible with parturitions in winter, and milk yield is not affected by reduced annual precipitation in rangelands of northern Mexico. Offspring growth performance depends on maternal milk yield, but not milk composition. Nevertheless, slow growth to weaning of offspring had adverse effects on time to reach adequate market weight.

Performance of dairy cows fed diets formulated at 2 starch concentrations with either canola meal or soybean meal as the protein supplement.

This study was designed to evaluate the effects of substituting corn grain with nonforage fiber sources in diets containing soybean meal (SBM) or canola meal (CM) as the primary protein source. Sixteen Holstein cows were assigned to a replicated 4 × 4 Latin square design with 4 periods of 28 d each. Treatments were arranged as a 2 × 2 factorial with 2 protein sources (SBM and CM) and 2 dietary starch concentrations (21 and 27% dry matter, DM). Diets were formulated to contain 16.5% CP, and the 21% starch diets were obtained by replacing corn grain with soybean hulls and beet pulp. Protein source × starch interactions were observed for DM intake (DMI), milk fat and protein concentrations, milk protein yield, milk urea nitrogen, and feed efficiency. Cows fed CM diets had a higher DMI when dietary starch concentration was 27% compared with 21%, but those cows had DMI similar to that of cows on SBM diets regardless of the starch concentration. Milk fat percentage was decreased in cows fed CM with 27% starch compared with cows fed CM with 21% starch and cows fed SBM with 27% starch. Milk protein percentage and yield and milk lactose percentage were least in cows fed CM with 21% starch compared with the other 3 diets, but feed efficiency was greater for cows fed CM with 21% starch. Milk urea nitrogen was least in cows fed CM with 27% starch compared with the other 3 diets. Cows fed diets with 27% starch produced 2.5 kg/d more milk and 1.9 kg/d more energy-corrected milk compared with cows fed 21% starch. Digestibility of DM and organic matter was higher in cows fed SBM diets than in cows on CM diets, and cows fed 27% starch showed greater DM and organic matter digestibility than cows on 21% starch. Digestibility of neutral detergent fiber and acid detergent fiber was greater in diets with SBM than in those with CM. Molar proportion of acetate was the lowest for cows fed CM with 21% starch compared with cows fed SBM with 21% starch, with the remaining cows fed being intermediate and similar. However, propionate was highest for cows fed CM with 21% starch than for cows fed SBM with 21% starch, but the remaining treatments were intermediate and similar. Isobutyrate was greater for cows fed CM with 21% starch, which resulted in the lowest acetate:propionate ratio compared with cows fed the remaining treatments. Overall, we confirmed that the interaction of protein with starch in CM diets can sustain similar cow performance as with the SBM diets. Those making decisions about starch concentration and protein source should consider feed price when SBM or CM and different starch levels are being formulated in diets for lactating dairy cows.

Short communication: Meta-analysis of dairy cows fed conventional sorghum or corn silages compared with brown midrib sorghum silage.

A meta-analysis was conducted to compare the effects of feeding dairy cows conventional sorghum silage (CSS) or conventional corn silage (CCS) compared with brown midrib sorghum silage (BMRSS) diets on dry matter intake (DMI), milk production, and milk composition. Data from 9 published articles (1984 to 2015) were used to contrast diets with CSS (7 means comparisons; 104 cows) or CCS (13 means comparisons; 204 cows) versus BMRSS diets. Statistical analysis was performed using fixed or random effects models with the Metafor package of R (https://www.R-project.org). The degree of heterogeneity was measured with the I2 statistic, and publication bias was determined with funnel plots and Egger's regression test. Other sources of heterogeneity of response were analyzed through meta-regression. Estimated effect size was calculated for DMI, milk production, and milk composition. No evidence of publication bias was observed for any variable tested. The highest degree of heterogeneity (I2 = 41.5 and 72.6%) was observed for DMI among dependent variables tested in both comparisons, indicating that intake responses to silage type are rather inconsistent; in contrast, milk production had the lowest degree of heterogeneity (I2 = 0%), supporting the idea that the responses of this variable to silage type were very consistent across studies. Compared with BMRSS diets, cows fed CSS diets exhibited decreased milk production (1.64 kg/d), milk fat concentration (0.09%), milk fat yield (0.08 kg/d), milk protein yield (0.04 kg/d), and milk lactose yield (0.16 kg/d) and tended to decrease DMI (0.83 kg/d). Compared with CCS diets, cows fed BMRSS diets increased milk fat concentration (0.10%), but decreased milk protein concentration (0.06%) and tended to increase lactose yield (0.08 kg/d). Meta-regression indicated that days in milk affected DMI and milk production when CSS diets were compared with BMRSS diets, and DMI when CCS diets were compared with BMRSS diets. Additionally, the inclusion rate of silage in the diet and dietary neutral detergent fiber affected yields of milk fat and lactose, respectively, when CCS and BMRSS diets were compared. Overall, lactation performance improved when cows were fed diets formulated with BMRSS compared with CSS, but performance was not different for cows fed BMRSS and CCS diets. However, the small sample size may have influenced these results by increasing the margin of the error and, concurrently, the power of the meta-analysis. Results of this analysis suggest that additional research is needed to explore the effects of days in milk and the inclusion rates of silages in the diets when comparing BMRSS with CSS or CCS.