Cows that were subjected to hot environmental temperatures yielded less milk (3.1 kg/d) on a diet high in CP (18.4%) and of medium degradability (65%) than on diets high in CP of low degradability (59%) or medium in CP (16.1%). The high CP diets were associated with decreased DMI and higher water intake, ruminal NH4, and blood urea. Negative effects on yield from the high CP, medium degradability diet were not observed at moderate temperatures. Evaporative cooling of cows in hot weather resulted in a greater milk yield response to low versus medium rumen-undegradabale protein diets than for uncooled cows. Evaporative cooling of cows also affected response to protein quality. For cooled cows, high Lys diet (soybean, fish, and blood meals) increased milk yield 14% over that with low Lys diet (corn gluten meal), but, for uncooled cows, a high Lys diet only increased yield by 9%. Percentage of CP, degradability, and protein quality had no effect on body temperatures or respiration rates of lactating cows. Some, but not other, reports showed that supplementation of 2 to 2.5% fat to diets fed under hot summer conditions resulted in less yield response than when fat was added at moderate temperatures. In several studies, fungal cultures (3 to 5 g/d) in the diet decreased body temperatures and respiration rates in hot, but not cool, weather. Increased milk yields and cellulose digestibility also resulted from dietary fungal cultures in some, but not all, trials. The mechanism of action exerted by fungal cultures on body temperature and respiration rate is unclear.

Tallow, Ca salts of palm fatty acids, or prilled fatty acids were added at 2.5% to a control diet (3.7% fatty acids) containing 7.2% ammoniated whole cottonseed. Diets were fed to midlactation cows (6 cows per treatment) for 72 d to determine effects of fat supplementation and fat source on lactation performance and nutrient digestibilities. Dry matter intake did not differ among treatments. Milk yield was 31.6 kg/d for the control and increased an average of 2.1 kg/d with fat supplementation. Source of supplemental fat did not significantly affect lactation performance. Added fat decreased milk protein content but did not affect protein yield. Milk fat, lactose, and SNF contents did not differ among treatments. Overall fat supplementation did not affect digestibilities of DM, ADF, or NDF but decreased digestibility of fatty acids. Contribution of de novo fatty acids to milk fat was decreased with fat supplementation. Addition of 2.5% fat to a diet containing a medium amount of fat from whole cottonseed increased milk yield. Tallow, Ca salt of palm fatty acids, and prilled fatty acids did not differ in milk yield response.

Under hot summer conditions of Tucson, Arizona, 24 Holstein cows (mean = 80 d of lactation) were assigned for 56 d to four treatments in a randomized block design with a 2 x 2 factorial arrangement of treatments. Factors were 1) medium [4.6% of dry matter (DM)] versus high (7.4% of DM) amounts of dietary fat and 2) corral shade only versus shade equipped with evaporative cooling. The high fat diet contained 3% prilled fatty acids. The efficiency of the conversion of feed to milk tended to be better for cows fed prilled fat than for cows fed medium dietary fat, but other lactation measurements were unaffected. Cows with access to evaporative cooling had greater milk yields than did cows with access to shade only. Prilled fatty acids did not depress the percentage of milk protein, but reduced short- and medium-chain fatty acids (C6:0 to C14:0) in milk fat and increased palmitic acid. Digestibilities of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, and starch were unaffected by amount of fat or by cooling method, but prilled fatty acids tended to decrease apparent digestibility of fatty acids. No differences were observed among treatments in respiration rates or rectal temperatures. When rectal temperatures were determined, cows were crowded, which probably negated detection of an effect of evaporative cooling. Evaporative cooling increased milk yield of cows in hot weather, but the addition of 3% fatty acids did not increase yield, and no interactions were observed.

The objective of this study was to compare the relative feeding value of sorghum versus corn grain in rolled or steam-flaked forms in diets for lactating dairy cows. Twenty-four Holstein cows (averaging 110 DIM) were divided into four groups and fed diets of 40% grain as dry-rolled sorghum, steam-rolled corn, steam-flaked sorghum, or steam-flaked corn for 70 d. Compared with rolling, flaking of both grains increased yields of milk, milk protein and fat, and protein percentage of milk, but differences tended to be greater for sorghum than for corn. Efficiency of feed utilization was higher for steam-flaked than for dry-rolled sorghum but was unaffected by corn processing. Flaking of both grains increased total tract digestibilities of DM, OM, CP, starch, ADF, and NDF. Estimates for NEL were 21% higher for flaked than for rolled sorghum and 6% higher for flaked than for rolled corn. No differences in performance of cows existed between corn and sorghum grains. Cows fed 40% of their diet as steam-flaked sorghum or corn yielded more milk and milk protein than those fed the rolled form of the grains, and no differences existed between types of grain fed.

Thirty Holstein cows averaging 50 DIM were assigned to five dietary treatments for 75 d to determine the effects of source and amount of supplemental fat on milk yield, milk composition, and nutrient digestibilities. Diets were 1) control, 2) diet 1 plus 12% whole cotton-seed, 3) diet 2 plus 2.2% safflower oil, 4) diet 2 plus 2.2% prilled tallow fatty acids, and 5) diet 2 plus 4.4% prilled tallow fatty acids. Milk yield was increased an average of 2.1 kg/d by addition of 2.2% prilled tallow fatty acids or safflower oil to the diet (7% fatty acids) containing 12% whole cottonseed. However, when fatty acids were increased to 9.1% with additional prilled tallow fatty acids, milk yield, DMI, and fatty acid digestibility decreased. Whole cottonseed alone and in combination with all fat additions decreased milk protein concentrations. Safflower oil increased C18:0, C18:1, and C18:2 fatty acids in milk. Digestibilities of OM, NDF, and ADF were not affected by diet. Supplementation of a saturated or unsaturated fat source to increase fatty acid content to 7.0% of dietary DM increased milk yield, but a further increase in fat to 9.1% with the saturated source appeared excessive for cows yielding 30 to 35 kg/d of milk.

To vary ruminally degradable starch, sorghum grain was dry-rolled or steam-flaked to different densities and compared with dry-rolled barley in total mixed diets fed to 40 lactating cows (111 d of lactation) assigned to five dietary treatments. Diets contained (percentage of dry matter) 35% alfalfa hay, 4.1% cottonseed hulls, 10% whole cottonseed, 2% fish meal, 4% soybean meal, and 4.9% of a molasses, mineral, and vitamin supplement. Treatments were 40% sorghum grain either dry-rolled or steam-processed at flake densities of 437, 360, and 283 g/L. A fifth diet containing 42% dry-rolled barley was fed. Cows were blocked according to pretreatment (14 d) milk yield and received experimental diets for 56 d. Increasing ruminal starch degradability by including steam-flaked sorghum grain or barley in the diet did not increase milk yield or milk protein percentage and yield, as was shown in eight previous studies. Steam-flaked sorghum or dry-rolled barley in the diet decreased dry matter intake, resulting in a 10 to 19% higher efficiency of conversion of feed dry matter to milk than that for dry-rolled sorghum. Milk urea N was decreased, and milk casein yield tended to be increased, by steam-flaking sorghum at the moderate density compared with dry-rolling or fine flaking. Dietary protein was more efficiently converted to milk protein and casein from flaked sorghum and dry-rolled barley than from dry-rolled sorghum. In this study, increasing ruminal starch degradability resulted in higher feed efficiency and lower feed intakes, bu optimal flake densities for steam-processed sorghum gain to maximize milk and milk protein yield were not clarified.

The objective of this study was to determine the effects of steam-rolled versus steam-flaked corn in the diet with or without the addition of a culture of Aspergillus oryzae on the performance of high producing dairy cows during hot summer weather. Thirty-two Holstein cows averaging 92 (+/- 60) d in milk were fed a pretreatment diet for 21 d followed by a 70-d experimental period in a completely randomized block design with a 2 x 2 factorial arrangement of treatments. Diets were 1) steam-flaked corn plus 3 g/d of A. oryzae, 2) steam-flaked corn, 3) steam-rolled corn plus 3 g/d of A. oryzae, and 4) steam-rolled corn. Intake was not affected significantly by grain processing or addition of A. oryzae. Compared with effects from steam-rolled corn in the diet, steam-flaked corn increased milk production; percentage of milk protein; yields of milk protein, lactose, and SNF; and the efficiency of conversion of dry matter to fat-corrected milk. Addition of A. oryzae tended to increase protein percentage and increased the percentage of SNF. Changes in body weight and body condition score tended to be higher, and somatic cell count tended to be lower, for cows fed the flaked corn than for cows fed the rolled corn. No interactions were significant. Treatments did not affect rectal temperatures or respiration rates; however, high mean values measured at 1400 h once weekly indicated thermal stress. These data show improved milk production from cows fed steam-flaked corn but not from those fed diets supplemented with A. oryzae.

Forty-eight lactating Holstein cows averaging 81 d in milk were allotted to eight blocks based on milk yield during the 14-d pretreatment period and randomly assigned to six treatment groups in a 2 x 3 factorial arrangement of treatments for 64 d. Factors were type of sorghum grain processing [dry-rolled vs. steam-flaked; fed at 34% of dry matter (DM) in a total mixed ration (TMR) based on alfalfa] and type of supplemental fat (2.5% of DM as cottonseed oil, tallow, or prilled fatty acids). Compared with dry-rolled sorghum, steam-flaked sorghum did not affect milk yield, fat percentage, or fat yield but did increase milk protein percentage, body weight gains, and estimated net energy for lactation (22%). Fat source did not affect lactational response, but, compared with tallow, prilled fatty acids tended to decrease DM intake. Steam-flaked sorghum, compared with dry-rolled sorghum, increased digestibilities of DM, organic matter, crude protein, and starch, regardless of fat source. The TMR containing prilled fat had lower digestibilities of DM and organic matter than did TMR containing cottonseed oil or tallow; and TMR containing prilled fat had lower digestibilities of crude protein and total fatty acids than did TMR containing tallow. This study showed that steam-flaking of sorghum grain increased milk protein content, body weight gains, and estimated net energy for lactation, regardless of dietary fat source.