Methionine precursor effects on lactation performance of dairy cows fed raw or heated soybeans.

Two experiments were conducted to evaluate the effect of isopropyl ester of 2-hydroxy-4-(methylthio) butanoic acid (HMBi) on lactation performance of dairy cows. Experiment 1 evaluated the effect of HMBi in diets with 15.3% crude protein (CP) and with different proportions of rumen-degradable and undegradable protein. Variation in rumen-degradable and undegradable protein was achieved by replacing raw with heated soybeans. Experiment 2 was an on-farm trial to evaluate HMBi with a large number of observations and using a farm-formulated diet (17.2% CP). In experiment 1, 20 Holsteins at 100 ± 41 d in milk were allocated to 5 replicated 4 × 4 Latin squares with 21-d periods. Treatments were formed by a 2 × 2 factorial arrangement of raw or heated soybeans with or without HMBi. Paper capsules with HMBi were orally administered twice daily to each cow. Dosage of HMBi was 7.6 g of digestible Met/cow per day. There was no interaction between soybean type and HMBi. Heat-treated soybeans increased the yields of milk, protein, fat, and lactose, and reduced urea N in milk and plasma (PUN) compared with raw soybeans. Rumen microbial yield, dry matter intake (DMI), and the total-tract apparent digestibility of nutrients did not differ between soybean types. There was no evidence for HMBi-driven effects on DMI, milk and components yield, or diet digestibility. Urinary purine derivative excretion and PUN concentration were reduced in HMBi-fed cows compared with cows fed diets without HMBi. In experiment 2, 294 Holstein cows were blocked by parity and milk yield, and randomly assigned to HMBi (8.9 g of digestible Met/cow per day) or control. The final data set had 234 cows (215 ± 105 days in milk; 96 primiparous and 138 multiparous; 114 on control and 120 on HMBi) housed in 4 freestall groups (1 group/treatment per parity). The freestall group was the experimental unit for DMI, diet and orts composition, and feed availability. The HMBi supplement was top dressed for 28 d on the first daily meal of each cow, immediately after feed delivery of the same batch of feed to all 4 freestall groups (3 times per day). Sample collection and feed analysis occurred during the last 5 d. Spot urine samples and blood samples from each cow were obtained for analysis of the urinary allantoin to creatinine ratio and PUN. Feed availability, the contents of CP and neutral detergent fiber in diets and orts, and DMI did not differ. Cows fed with HMBi had greater milk protein yield and concentration compared with control and had no change in milk fat and lactose. Rumen microbial yield was greater and PUN was lower in HMBi-fed cows compared with control. In experiment 1, HMBi decreased rumen microbial yield and did not affect lactation performance, but it increased ruminal microbial yield and the secretion of milk protein in experiment 2. These results suggest that lactation response to HMBi may be partially mediated by ruminal events. Heated soybeans increased the efficiency of N utilization and the yields of milk, protein, fat, and lactose, but did not interact with HMBi supplementation.

Effect of kernel processing and particle size of whole-plant corn silage with vitreous endosperm on dairy cow performance.

Kernel processing and theoretical length of cut (TLOC) of whole-plant corn silage (WPCS) can affect feed intake, digestibility, and performance of dairy cows. The objective of this study was to evaluate for lactating dairy cows the effects of kernel processing and TLOC of WPCS with vitreous endosperm. The treatments were a pull-type forage harvester without kernel processor set for a 6-mm TLOC (PT6) and a self-propelled forage harvester with kernel processor set for a 6-mm TLOC (SP6), 12-mm TLOC (SP12), and 18-mm TLOC (SP18). Processing scores of the WPCS were 32.1% (PT6), 53.9% (SP6), 49.0% (SP12), and 40.1% (SP18). Twenty-four Holstein cows (139 ± 63 d in milk) were blocked and assigned to six 4 × 4 Latin squares with 24-d periods (18 d of adaptation). Diets were formulated to contain 48.5% WPCS, 15.5% citrus pulp, 15.0% dry ground corn, 9.5% soybean meal, 6.8% low rumen degradability soybean meal, 1.8% calcium soap of palm fatty acids (FA), 1.7% mineral and vitamin mix, and 1% urea (dry matter basis). Nutrient composition of the diets (% of dry matter) was 16.5% crude protein, 28.9% neutral detergent fiber, and 25.4% starch. Three orthogonal contrasts were used to compare treatments: effect of kernel processing (PT6 vs. SP6) and effect of TLOC (particle size; SP6 vs. SP12 and SP12 vs. SP18). Cows fed SP6 produced 1.2 kg/d greater milk yield with no changes in dry matter intake, resulting in greater feed efficiency compared with PT6. Cows fed SP6 also produced more milk protein (+36 g/d), lactose (+61 g/d), and total solids (+94 g/d) than cows fed PT6. The mechanism for increased yield of milk and milk components involved greater kernel fragmentation, starch digestibility, and glucose availability for lactose synthesis by the mammary gland. However, cows fed SP6 had lower chewing time and tended to have greater levels of serum amyloid A compared with PT6. Milk yield was similar for SP6 and SP12, but SP12 cows tended to have less serum amyloid A with greater chewing time. Cows fed SP18 had lower total-tract starch digestibility and tended to have lower plasma glucose and produce less milk compared with cows fed SP12. Compared with PT6, feeding SP6 raised linear odd-chain FA concentration in milk. Similarly, a reduction of these same FA occurred for SP12 compared with SP6. Cows fed SP6 had greater proportion of milk C14:1 and C16:1 compared with PT6 and SP12. Lesser trans C18:1 followed by greater C18:0 concentrations were observed for SP12 and PT6 compared with SP6, which is an indication of more complete biohydrogenation in the rumen. Under the conditions of this study, the use of a self-propelled forage harvester with kernel processing set for a 12-mm TLOC is recommended for WPCS from hybrids with vitreous endosperm.

The effect of length of storage and sodium benzoate on the nutritive value of reconstituted sorghum grain silages for dairy cows.

Twenty Holstein cows at 168 ± 87 d in milk (mean ± SD) were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement to evaluate the effects of 2 storage lengths (30 or 90 d) and the presence of sodium benzoate (control or 0.2% as fed) on the nutritive value of reconstituted sorghum grain silages (RSGS). For each treatment, dry ground sorghum grain was rehydrated to 35% moisture and ensiled in 200-L plastic drums. The treatments were RSGS stored for 30 d without sodium benzoate (30 CON), RSGS stored for 30 d with sodium benzoate (30 BEN), RSGS stored for 90 d without sodium benzoate (90 CON) and RSGS stored for 90 d with sodium benzoate (90 BEN). Diets contained 16.3% RSGS. Silages stored for 90 d had higher concentrations of 1,2-propanediol, soluble protein, and ammonia nitrogen than did those stored for 30 d. Sodium benzoate reduced ethanol and ethyl-ester formation. Silages stored for 90 d had higher starch (89.3 vs. 86.9%) and protein (57.1 vs. 54.0%) digestibility compared with silages stored for 30 d. The ruminal acetate-to-propionate ratio tended to be lower in RSGS stored for 90 d than in RSGS stored for 30 d (3.75 vs. 3.34). Milk yield increased from 30.0 kg/d in cows fed RSGS stored for 30 d to 31.2 kg/d in cows fed RSGS stored for 90 d, without a change in dry matter intake (23.5 kg/d on average). Hence, feed efficiency and milk N efficiency also had tendencies to increase in cows fed RSGS stored for 90 d. Sodium benzoate did not alter cow performance but slightly increased plasma glucose (65.2 vs. 63.6 mg/dL). In conclusion, increasing the storage period of RSGS from 30 to 90 d improved starch and protein digestibility, milk yield, and feed efficiency.

Relationship between processing score and kernel-fraction particle size in whole-plant corn silage.

Kernel processing increases starch digestibility in whole-plant corn silage (WPCS). Corn silage processing score (CSPS), the percentage of starch passing through a 4.75-mm sieve, is widely used to assess degree of kernel breakage in WPCS. However, the geometric mean particle size (GMPS) of the kernel-fraction that passes through the 4.75-mm sieve has not been well described. Therefore, the objectives of this study were (1) to evaluate particle size distribution and digestibility of kernels cut in varied particle sizes; (2) to propose a method to measure GMPS in WPCS kernels; and (3) to evaluate the relationship between CSPS and GMPS of the kernel fraction in WPCS. Composite samples of unfermented, dried kernels from 110 corn hybrids commonly used for silage production were kept whole (WH) or manually cut in 2, 4, 8, 16, 32 or 64 pieces (2P, 4P, 8P, 16P, 32P, and 64P, respectively). Dry sieving to determine GMPS, surface area, and particle size distribution using 9 sieves with nominal square apertures of 9.50, 6.70, 4.75, 3.35, 2.36, 1.70, 1.18, and 0.59 mm and pan, as well as ruminal in situ dry matter (DM) digestibilities were performed for each kernel particle number treatment. Incubation times were 0, 3, 6, 12, and 24 h. The ruminal in situ DM disappearance of unfermented kernels increased with the reduction in particle size of corn kernels. Kernels kept whole had the lowest ruminal DM disappearance for all time points with maximum DM disappearance of 6.9% at 24 h and the greatest disappearance was observed for 64P, followed by 32P and 16P. Samples of WPCS (n=80) from 3 studies representing varied theoretical length of cut settings and processor types and settings were also evaluated. Each WPCS sample was divided in 2 and then dried at 60 °C for 48 h. The CSPS was determined in duplicate on 1 of the split samples, whereas on the other split sample the kernel and stover fractions were separated using a hydrodynamic separation procedure. After separation, the kernel fraction was redried at 60°C for 48 h in a forced-air oven and dry sieved to determine GMPS and surface area. Linear relationships between CSPS from WPCS (n=80) and kernel fraction GMPS, surface area, and proportion passing through the 4.75-mm screen were poor. Strong quadratic relationships between proportion of kernel fraction passing through the 4.75-mm screen and kernel fraction GMPS and surface area were observed. These findings suggest that hydrodynamic separation and dry sieving of the kernel fraction may provide a better assessment of kernel breakage in WPCS than CSPS.

Response of lactating cows to live yeast supplementation during summer.

Dairy cows experiencing heat stress have reduced intake and increased reliance on glucose, making feeding strategies capable of improving diet digestibility plausible for improving postrumen nutrient flow and performance. The effect of yeast on digestion and performance of lactating cows during the warm summer months of southeastern Brazil was evaluated. Cows were individually fed in tie stalls and temperature-humidity index was above 68 during 75.6% of the experiment. Twenty-eight Holstein cows (207±87 d in milk) received a standard diet for 14 d and then a treatment for 70 d, in a covariate-adjusted, randomized block design with repeated measures over time. Treatments were yeast (Saccharomyces cerevisiae) or control. Yeast was top dressed to the diet in the morning, equivalent to 25×10(10) cfu of live cells and 5×10(10) cfu of dead cells. The diet contained corn silage (37.7%), Tifton silage (7.1%), raw soybeans (4.1%), soybean meal (16.5%), finely ground corn (20.7%), and citrus pulp (11.9%). Yeast increased milk (26.7 vs. 25.4 kg/d) and solids yield (3.06 vs. 2.92 kg/d), especially lactose. Response in milk yield was consistent over time and started at d 5. The daily intake of digestible OM, total-tract digestibility of nutrients, urinary allantoin excretion, chewing pattern throughout the day, and dry matter intake did not respond to yeast. A trend was observed for increased plasma glucose with yeast (62.9 vs. 57.3mg/dL), lowered respiratory frequency (48 vs. 56 breaths/min), and increased plasma niacin content (1.31 vs. 1.22 µg/mL), though cows had similar rectal temperature. Ruminal lactate and butyrate as proportions of ruminal organic acids were reduced by yeast, but no effects on other organic acids, ruminal pH, or protozoa content were detected. Plasma urea N over 24h was increased by yeast. On d 72 to 74, citrus pulp was abruptly replaced with finely ground corn to induce acidosis. The increased load of starch increased dry matter intake between 0700 and 1300 h, jugular blood partial pressure of CO2, HCO3-, and base excess, and decreased blood pH for both treatments. The yeast treatment had a higher blood pH compared with the control, 7.34, and 7.31, respectively. Yeast supplementation improved lactation performance of dairy cows under heat stress. Improvement in lactation performance apparently involved the regulation of body homeothermia, rather than improved digestibility.