Milk production and composition responses to the source of protein supplements in diets containing wheat middlings

Two 3 x 3 Latin square trials were conducted to determine the effect of the source of supplemental protein in diets containing wheat middlings on milk production and composition. Cottonseed meal or meat and bone meal was substituted for a portion of the soybean meal and provided 24.5% of the total dietary crude protein. Trial 1 was conducted during fall 1989, and trial 2 was conducted during summer 1993. During trial 1, no differences in production or composition of milk were found for primiparous cows fed the various protein supplements. Multiparous cows tended to have higher dry matter intakes and produced more milk with lower milk fat percentages when fed meat and bone meal than when fed soybean meal or cottonseed meal. No differences were found among supplements for other milk components or for the production of energy-corrected milk. In trial 2, primiparous cows tended to produce more milk, and multiparous cows tended to produce less milk, when fed meat and bone meal than when fed soybean meal. No differences were found for dry matter intake, milk composition, or production of energy-corrected milk. Cottonseed meal was equal to soybean meal in supporting milk production. Meat and bone meal tended to support higher productions of milk than did soybean meal, but production of energy-corrected milk was similar for both.     

Serum folic acid in anticonvulsant long term therapy (author''s transl)

Forty Holstein heifer calves were assigned at random among four dietary treatments: 1) an all-concentrate ration; 2) a pelleted complete ration of 20% alfalfa and 80% concentrate; 3) concentrate and alfalfa pellets fed separately, free-choice; and 4) concentrate and long-stem alfalfa hay fed separately, free-choice. Treatment diets were continued for 12 wk. Calves fed the concentrate only had reduced weight gains, feed intakes, and poorer feed efficiencies compared to treatments 2 and 4. Calves fed long-stem alfalfa hay as a roughage consumed more feed and had larger weight gains than calves fed alfalfa pellets as a roughage free-choice. The pelleted complete ration containing 20% alfalfa was comparable to a ration containing long-stem alfalfa hay free-choice for weight gains and feed efficiencies. The digestibility of dry matter and crude protein of the pelleted complete feed was similar to the digestibility of equal amounts and proportions of concentrate and alfalfa pellets fed separately. Thus, when fed free choice to early-weaned calves, pelleted alfalfa is inferior to long-stem hay for stimulating intake of dry matter. However, increasing the proportion of alfalfa pellets in a complete ration compensates for its partial loss of efficacy for elevating feed intake and growth rates.     

Effect of degradability of dietary protein and fat on ruminal, blood, and milk components of Jersey and Holstein cows

Twelve Holstein cows and 12 Jersey cows were used in six 4 x 4 Latin squares to investigate the effects of the degradability of dietary protein and supplemental dietary fat on milk components. Dietary dry matter contained 16% crude protein with two concentrations of ruminally undegradable protein (RUP) obtained by substituting blood meal for a portion of the soybean meal. Treatments were 1) 29% RUP, 0% added fat; 2) 29% RUP, 2.7% added fat (Ca soaps of fatty acids); 3) 41% RUP, 0% added fat; and 4) 41% RUP, 2.7% added fat. The dry matter of the total mixed ration fed at 1000 and 1400 h consisted of 30% corn silage, 29% alfalfa haylage, and 41% concentrate. Supplemental dietary fat depressed dry matter intake by 6.2%. Plasma urea N was greater at 0700 and 1600 h for Jerseys fed diets containing added fat and greater at 0700 h for Holsteins fed diets containing 41% RUP than for Holsteins fed 0% added fat and 29% RUP. When averaged across both breeds, milk production increased 7.1%, and production of 4% fat-corrected milk by Jerseys increased 8.4%, in response to added dietary fat. Milk protein was reduced when Holstein diets contained 41% RUP. Milk protein content was reduced 7.1 and 3.9%, and milk urea N was increased 4.9 and 8.5%, by added fat and 41% RUP in both breeds, respectively. Added fat reduced the concentration, but not the yield, of milk components. Substitution of blood meal decreased the concentration and yield of milk protein and casein N.     

Plasma amino acids of infants consuming soybean proteins with and without added methionine

Fasting plasma free amino acids were determined in 54 convalescent malnourished infants: seven infants while consuming a diet based on isolated soybean protein, containing 4.0% to 5.3% of dietary metabolizable energy (calories) as protein (A), 20 at 6.4% to 6.7% protein calories (B), 23 at 6.4% to 6.7% protein calories with added DL-methionine (C), and four with 8.0% to 12.3% protein calories (D). There were no differences in total amino acid concentration (TAA) among the four groups; the molar fraction of essential amino acids (EAA:TAA) was lower for group A; there were no differences among the four groups in Lys:EAA or 1/2 cystine:EAA ratios or in Met concentration. Met:EAA was higher in C than B, with considerable overlap of individual values. In 10 of 13 infants who were represented in both B and C, Met concentration and Met:EAA ratio were higher in group C. Fasting plasma AA levels are not consistently reliable for field or clinical assessment of dietary Met adequacy. Fasting and postprandial (3- and 4-hour) plasma AA were determined in 29 infants: in 12 the preceding diet and the test meal were both Met-deficient with less than 6.7% protein calories (E), in five the preceding diet was milk-based but the test meal was Met-deficient at less than 6.7% (F), in five the preceding diet and test meal were based on isolated soybean protein at less than 6.7% with DL-Met added (G), and in seven the test meal was soy-based with greater than 9.0% protein calories (H). Plasma Met concentration and Met:EAA fell significantly at 3 and 4 hours in groups E and F, but not in groups G and H, suggesting that a postprandial fall in Met:EAA ratio can be used to identify dietary Met deficiency in field situations.     

Evaluation of the digestibility of nutrients in pigs by ileal cannulation technique

A simple T-cannula was surgically inserted into the ileum of growing female Large White x Dutch Landrace swine. Chymus samples collected with the help of the cannula were analysed to determine the apparent digestibility of different dietary nutrients such as dry matter, crude protein and starch, as well as of some essential amino acids. The following three experiments were conducted: (I) of the cereals, the "Tewo" triticale variety fed alone and in 1:1 concentrate mixtures with wheat or maize was studied; (II) waxy maize hybrids and maize hybrids of normal endosperm were compared without treatment and after treatment by the Bocchi technology; (III) untreated and extruded maize supplemented either with extracted soybean or with extracted sunflower was also tested. The ileal digestibility of protein, amino acids and starch was determined and compared with values obtained by conventional (faecal) analysis. When feeding triticale alone or in combination with wheat or maize, the ileal digestibility of crude protein and amino acids increased as a result of feeding the cereal combinations (e.g. crude protein 72-79%, lysine 75-79%, threonine 63-78%, methionine 74-86%). Comparison of the two maize hybrids revealed that, with the exception of methionine, lysine and tyrosine, the amino acids of the waxy hybrid had higher ileal digestibility. Treatment of the normal hybrid by the Bocchi technology caused a significant improvement in the ileal digestibility of cystine, isoleucine, lysine, valine, and dry matter. This treatment also improved the faecal digestibility of all test nutrients but methionine. Bocchi treatment of the waxy hybrid significantly improved the ileal digestibility of isoleucine, leucine, methionine, tyrosine and valine, and the faecal digestibility of cystine, dry matter, and crude protein. No major variety- or treatment-related differences were found in the digestibility of starch. As a result of extrusion, the digestibility of nutrients of the soybean + maize mixture increased from 61.6% to 70.3% (crude protein), from 41.1% to 59.4% (threonine), from 60.1 to 72.0% (methionine), and from 70.7% to 82.7% (lysine). The same treatment of the sunflower + maize mixture increased the digestibility of crude protein from 80.6% to 84.5%, that of threonine from 78.1% to 80.6%, that of methionine from 79.7% to 84.3%, while that of lysine from 61.4% to 72.3%. The ileal digestibility of starch was 97-98% for both mixtures. As a result of extrusion, most of the faecal digestibility values showed a significant improvement for both the soybean- and the sunflower-containing mixtures. The favourable effect exerted by extrusion on the digestibility of nutrients is markedly influenced by the feed components.     

Intake, milk yield, and digestion by dairy cows fed diets with increasing fiber content from bermudagrass hay of silage

Lactating dairy cows were offered diets containing increasing quantities of Tifton 85 bermudagrass hay or silage and increasing dietary neutral detergent fiber (NDF) to determine effects of method of bermudagrass storage and dietary fiber content on intake, milk yield, and nutrient digestion. Bermudagrass was added as hay or silage at the rate of 8.5, 15.9, or 23.3% of dietary dry matter and was substituted for an equal quantity of corn silage. The method of bermudagrass storage did not affect intake [20.8 vs. 20.3 (+/- 0.3) kg/d for bermudagrass hay and silage diets; respectively], but an increase in the amount of bermudagrass and NDF in the diet did reduce intake. Dietary NDF concentration was well above minimum recommendations of the National Research Council. Milk yield was not altered by method of bermudagrass storage but declined as dietary NDF increased. Digestion of NDF tended to be lower for bermudagrass silage than for bermudagrass hay. An increase in the amount of bermudagrass in the diet improved digestion of dietary dry matter, acid detergent fiber, and NDF; however, milk yield declined because total intake declined. Improved NDF digestion caused by added bermudagrass hay or silage was confirmed by in vitro analyses. High quality bermudagrass hybrids could potentially be used in diets of lactating dairy cows because of the good digestion characteristics and relatively small effects on intake despite the high dietary fiber content. Tifton 85 bermudagrass may serve as a forage alternative for lactating dairy cows.     

Secretion of endogenous amino acids in the gastrointestinal tract and amino acid resorption in the swine

A trial was performed with 2 fistula pigs (each with 2 fistulas, one located about 30 cm below the pyloric orifice and the other at the end of the small intestine). Animal A received a casein diet containing 14% crude protein for a period of 2 weeks before the tracer amino acid was administered. Animal B received the same diet for a period of 10 days and was then fed a diet (at the same protein level) containing gluten as sole protein source. The two tracer amino acids, 14C-U-L-leucine and 3H-4,5-(N)-L-lysine, were injected intravenously. The passage rates for dry matter, organic matter and N measured at the beginning of the small intestine were higher than the rate of intake. The rate of passage of amino acids was also found to be increased relative to the rate of intake. In general, this increase involved the non-essential amino acids to a much larger extent. A considerable proportion of the amino acids passing into the large intestine is not excreted with the faeces but is probably converted in catabolic processes. It is for this reason that any values for the efficiency of amino acid absorption calculated on the basis of data on the faecal excretion of amino acids will not provide conclusive evidence for the availability of dietary amino acids in processes of the intermediate metabolism. The rate of secretion of 3H and 14C radioactivity into the digesta of the small intestine was found to increase rapidly within 1-2 hrs after administration of the tracer amino acids. The 14C radioactivity detected was found to be almost exclusively derived from 14C leucine while only about 60% of the 3H activity found in the digesta of fistula I were shown to be bound to lysine. Labelled lysine and leucine (of endogenic origin) are absorbed into the small intestine at a slower rate (i.e. endogenic proteins are less efficiently digested) than the non-radioactive amino acids (of exogenic origin) so that a process of concentration of endogenic amino acids is observed towards the end of the small intestine.     

Effect of amount of dietary supplement and source of protein on milk production, ruminal fermentation, and nutrient flows in dairy cows

An experiment with a multiple Latin square design using 36 midlactation Friesian cows was carried out to determine the effect of fish meal or soybean meal in a supplement fed at two amounts (3.5 or 7 kg/d) with grass silage. The diets were also fed to four ruminally and duodenally cannulated cows to determine digestibility, ruminal fermentation, and nutrient flows. Dry matter intake, milk production, milk constituent yields, and concentrations of protein and lactose were significantly increased by the supplements when provided at 7 kg/d. The supplement containing fish meal increased milk production, protein and lactose yields, and milk protein concentration, but the increases were smaller than those obtained by increasing the amount of supplement fed. Neither the type nor the amount of supplement fed affected digestibility of dry matter or organic matter, and few significant effects on ruminal fermentation were observed. Supplements fed at the higher allowance significantly increased the flow of dry matter, organic matter, all nitrogenous components, and amino acids to the duodenum. The supplement containing fish meal significantly increased the duodenal flow of nonammonia nonmicrobial N and some amino acids. Results indicated that an increase in the concentration of supplement in the diet is more effective in increasing milk production, protein concentration and yield, and flow of amino acids to the duodenum than is increasing the concentration of ruminally undegradable protein in the supplement.     

Effects of dietary supplementation on nutrient digestion and the milk yield of intensively grazed lactating dairy cows

Fourteen midlactation Holstein cows were used in an 80-d study to examine supplementation strategies during intensive rotational grazing. Factors examined were the concentration of protein in the supplement [12 or 16% crude protein (CP) on a dry matter basis] and the amount of supplement offered (6.4 or 9.6 kg/d per cow). The supplement was offered in equal portions three times daily after milking. Pasture, composed of alfalfa (Medicago sativa) and orchardgrass (Dactylis glomerata), was divided into 27 0.16-ha paddocks that were grazed for 12 to 24 h. Intake of forage tended to increase as CP in the supplement increased but was unaffected by the amount of supplement offered. Intakes of organic matter and dry matter and the digestion of these nutrients in the total tract increased as CP in the supplement increased and as the amount of supplement increased. Ruminal pH and concentrations of volatile fatty acids were unaffected by treatments, but concentrations of NH3 N increased as CP in the supplement increased. An increase in CP resulted in a greater intake and flow of total N to the duodenum. The flow of microbial N to the duodenum and the efficiency of microbial protein synthesis were unaffected by treatment. Flows of total amino acids and essential amino acids to the duodenum tended to increase as CP in the supplement increased. Yield of fat-corrected milk and concentrations of fat and protein in milk were unaffected by treatment. These results suggested that the supply and digestion of nutrients in grazing dairy cows may be improved through an increase in the CP concentration of the supplement or the amount of supplement offered. However, effects on the yield of milk and milk components may be small.     

Fatty acid composition of milk from Holstein cows fed oleamide or canola oil

Based on previous in vitro results that showed reduced biohydrogenation of oleamide by ruminal microbes, this study was conducted to determine whether the addition of oleamide to the diets of dairy cows would enhance the C18:1 concentration in milk. Nine first lactation Holstein cows were fed three diets in a 3 x 3 Latin square replicated three times. Each period lasted 3 wk. The total mixed diets consisted of 42% corn silage and 58% concentrate (dry matter basis) with either no added fat (control), 3.5% high oleic canola oil, or 3.5% oleamide. Dry matter intake was reduced when oleamide was added to the diet but not when canola oil was added. Milk yields were the same for cows fed all three diets. Canola oil reduced fat-corrected milk yield and milk fat concentration, but these were not affected by oleamide. Milk protein concentration was lower for cows fed oleamide than for cows fed canola oil. Milk C18:1 averaged 23.16% of total fatty acids for cows fed the control diet and increased to 35.13% when canola oil was fed. Oleamide further increased C18:1 to 48.16% of total fatty acids in milk. All fatty acids with > or = 16 carbon chain length were reduced by oleamide. Oleamide was more effective than was canola oil in this study at increasing the oleic acid content of bovine milk. Oleamide reduced dietary intake when added at 3.5% of the dietary dry matter but still had no effect on milk yield or milk composition.     

Supplementation of milk replacers containing soy protein with threonine, methionine, and lysine in the diets of calves

An attempt was made to improve the protein quality supplied in milk replacers containing soy protein by supplementing Thr, Met, and Lys to the milk replacers fed to calves. Six Holstein x indigenous male calves were fitted with single cannulas at the end of the ileum. Calves were fed milk replacers containing skim milk (86%) and whey (14%) proteins or skim (43%), whey (14%), and soy (43%) proteins either with or without amino acid (AA) supplementation according to a double 3 x 3 Latin square design. Average daily gain, N retention, and ileal digestibilities of dry matter, N, and AA were significantly higher for calves fed the milk replacer containing skim milk protein than for calves fed the milk replacer containing soy protein. Average daily gain, N retention, and ileal digestibilities of dry matter, N, and AA were significantly higher for calves fed the milk replacer containing soy protein plus AA supplementation than for calves fed the milk replacer containing the soy protein without AA supplementation. Therefore, supplementation of a milk replacer containing the soy protein without AA supplementation. Therefore, supplementation of a milk replacer containing soy protein with limiting AA that correspond to the AA found in milk protein can considerably improve the protein quality of that milk replacer for the preruminant calf.     

Decreased dietary protein or energy intake and plasma growth hormone levels of the pregnant pig, its fetuses and developing progeny

The effects of low protein diets on plasma growth hormone were studied in pregnant pigs, fetuses and the developing progeny. Pregnant pigs were fed 18%, 3% or 0.5% protein diet throughout the gestation period. At 10, 13 and 15 week of gestation, fetuses were removed from the uterus after the dam had been bled to death. Plasma samples were used for growth hormone determinations. In a second experiment, 2-day old pigs from another set of pregnant pigs fed the diet containing 18%, 3% or 0.5% protein during gestation were cross-fostered to control nursing dams and weaned at 4 weeks of age to a standard diet. Plasma obtained at regular intervals was used for growth hormone determination. Plasma growth hormone was significantly higher in dams fed 0.5% protein after week 13 of gestation. High growth hormone (ten times the dam GH level) was observed in all fetuses irrespective of maternal dietary manipulation. Offspring of severely protein deprived pits (0.5% protein) had significantly elevated growth hormone levels up to 12 weeks of age in spite of cross fostering to a control dam after birth. The data suggest that there is little or no effect of maternal protein restriction on fetal growth hormone levels but the persistent high growth hormone levels in the progeny of severely malnourished pigs indicate a possible impairment of the production, release or catabolism of growth hormone and/or its releasing factor.     

Effect of lean growth genotype and dietary amino acid regimen on the lactational performance of sows

The effect of dietary amino acid regimen and genetic capacity for lean tissue growth on the lactational performance of sows was determined in primiparous sows with a high (350 to 390 g/d) or low (240 to 280 g/d) genetic capacity for lean tissue growth from 18 to 110 kg of body weight. During lactation, sows were offered daily 6.5 kg of one of four fortified corn-soybean meal diets containing .58, .77, .96, and 1.15% lysine (L). Litters were standardized to 14 pigs within 8 h after birth. On d 2 of lactation, the high lean growth (LG) sows possessed more proteinaceous tissues and protein and less fat tissue and lipid. During lactation (d 2 to 28 postpartum), high LG sows consumed more feed, mobilized more body protein, and lost less body lipid. Milk, milk energy, and milk lysine yields (pooled across dietary regimens) were similar between genotypes. As daily dietary lysine intakes increased from 27 to 62 g and total digestible lysine supplies (from diet and mobilized tissues) increased from 39 to 68 g, daily yields of milk, milk energy, and milk lysine increased, but the magnitude of the response differed (P < .05) between genotypes, evidently because of differences in the ability of the high and low LG sows to mobilize energy from body tissue. Based on these data, the lactational capacities of high and low LG sows nursing 12 to 14 pigs are similar when similar supplies of lysine and energy are available from dietary intake and mobilized body tissue stores. When supplies of ME do not limit milk synthesis, daily digestible lysine intakes of at least 54 g (> or = 66 g from a corn-soy diet) are needed by these sows nursing litters of 12 to 14 pigs to support milk synthesis and minimize maternal protein losses. This is equivalent to a total digestible lysine need of 4.3 to 4.6 g/kg of milk produced. When ME provided by the diet is less than that needed to fuel maximum milk synthesis, however, the dietary amino acid needs of genetically lean sows may be reduced because of their inability to mobilize sufficient body fat stores.     

Maternal dietary protein deficiency decreases nitric oxide synthase and ornithine decarboxylase activities in placenta and endometrium of pigs during early gestation

Little is known about the mechanism responsible for retarded placental and fetal growth induced by maternal dietary protein malnutrition. On the basis of the recent finding that nitric oxide (NO) and polyamines (products of L-arginine) play an important role in embryonic and placental development, the present study was designed to determine whether protein deficiency decreases placental and endometrial activities of NO synthase (NOS) and ornithine decarboxylase (ODC) (the first and key regulatory enzyme in polyamine synthesis). Primiparous gilts selected genetically for low or high plasma total cholesterol concentrations (low line and high line, respectively) were mated and then fed 1.8 kg/d of isocaloric diets containing 13% or 0.5% crude protein. At d 40 or 60 of gestation, they were hysterectomized, and placenta and endometrium were obtained for incubations, NOS and ODC assays, and measurements of free amino acids and polyamines. Maternal dietary protein restriction decreased arginine and ornithine concentrations, constitutive and inducible NOS activities and NO production, as well as ODC activity and polyamine concentrations in placenta and endometrium of both lines of gilts. Placental NO synthase activity and NO generation were lower in high line gilts than in low line gilts. ODC activities and polyamine concentrations in placenta and endometrium were decreased at d 60 compared with d 40 of gestation. These changes in placental and endometrial synthesis of NO and polyamines during early gestation may be a mechanism responsible for reduced placental and fetal growth in protein-deficient gilts and for altered conceptus development in high line gilts.     

Relationships between nutrition and foraging behavior of free-ranging sheep and goats

Goats generally tolerate dry season forage conditions in northeastern Brazil's tropical deciduous woodland better than sheep do, but the mechanisms underlying sheep and goat response to wet and dry season conditions are not well understood. We evaluated aspects of nutrition and behavior of free-ranging sheep and goats in this woodland to improve our understanding of these mechanisms. Body weight changes, dietary botanical and chemical composition, and daily activities were measured for sheep and goats that foraged in this woodland during four defined periods of a year. Vegetation available to these animals was also measured. Although there was much less available vegetation during the wet season than during the dry season, body weights and dietary crude protein content of sheep and goats increased during the wet season and decreased during the dry season. During the four periods of the year, weight changes of sheep, and possibly those of goats, were positively related to the content of crude protein in their diets. Foraging times of sheep and goats were generally greater during the dry season than during the wet season and were positively related to available browse and inversely related to dietary crude protein content. Sheep and goats may have foraged longer during the dry periods because they were spending more time searching through the large quantity of low-quality vegetation for dietary items with relatively higher levels of crude protein.     

Maternal dietary protein deficiency decreases amino acid concentrations in fetal plasma and allantoic fluid of pigs

This study was conducted to test the hypothesis that maternal dietary protein deficiency decreases amino acid availability to the fetus, thereby contributing to retarded fetal growth. Primiparous gilts selected genetically for low or high plasma total cholesterol concentrations (low line and high line, respectively) were mated, and then fed 1.8 kg/d of isocaloric diets containing 13% or 0.5% crude protein. At d 40 or 60 of gestation, they were hysterectomized, and maternal and fetal blood samples as well as amniotic and allantoic fluids were obtained for analyses of amino acids, ammonia and urea. Dietary protein restriction decreased (P < 0.05) the following: 1) maternal plasma concentrations of urea at d 40 and 60 of gestation; 2) fetal plasma concentrations of alanine, arginine, branched-chain amino acids (BCAA), glutamine, glycine, lysine, ornithine, proline, taurine, threonine and urea at d 60 of gestation; 3) amniotic and allantoic fluid concentrations of urea at d 40 and 60 of gestation; and 4) allantoic fluid concentrations of alanine, arginine, BCAA, citrulline, cystine, glycine, histidine, methionine, proline, serine, taurine, threonine and tyrosine at d 40 of gestation, in gilts of both genetic lines. At d 60 of gestation, protein deficiency decreased (P < 0.05) allantoic fluid concentrations of arginine, cystine, glycine, taurine and tyrosine in low line gilts and of cystine, glutamine, ornithine, serine, taurine and tyrosine in high line gilts. Low line and high line gilts also differed remarkably in allantoic fluid concentrations of arginine, glutamine, ornithine and ammonia at d 40 and 60 of gestation. Our results suggest the following: 1) protein-deficient gilts maintain maternal plasma concentrations of amino acids by mobilizing maternal protein stores and decreasing oxidation of amino acids during the first half of gestation; 2) protein deficiency may impair placental transport of amino acids from the maternal to the fetal blood; and 3) low line and high line gilts differ in fetal amino acid metabolism. Decreases in concentrations of the essential and nonessential amino acids in the fetus may be a mechanism whereby maternal dietary protein restriction results in fetal growth retardation.     

Protein and methionine hydroxy analog for lactating cows

A 2 X 2 factorial experiment (protein 12.5 and 15.5; methionine hydroxy analog 0 and .125% dry matter) included 144 cows for one complete lactation, distributed over seven locations. Rations were formulated to the desired protein, methionine analog, and constant amounts of fiber 17%, sulfur .225%, calcium .6%, phosphorus .4%, and salt .5%. Treatment effects were not apparent for dry matter intake, daily milk and fat-corrected milk production, conversion of energy, and body weight changes. Conversion of dietary crude protein into milk protein was 34.5% for the low and 25.8% for the high protein ration. Methionine analon (0% = 2.54; .125% = 1.90). Effect of methionine analog was most apparent at low protein as 0 analog cows produced 247 kg fat, required 2.9 services/contraception, and had 156 days open whereas cows on other treatments (.125% analog and/or high protein) produced 264 kg fat, required 1.8 to 2.2 services/conception, and had 124 to 134 days open. Methionine analog response is discussed in relation to tuminal and postruminal effects as well as the interrelation with protein and energy.     

Adequacy of amino acids in diets fed to lactating dairy cows

The Cornell Net Carbohydrate and Protein System was used to evaluate absorbable limiting amino acids (AA) for milk yield. The system was utilized to characterize whether diets in five previous experiments met AA requirements for milk protein synthesis. Twenty-nine treatment means for milk yield from 367 cows constituted the database for the evaluation. Using the mechanistic relationships of nutrient metabolism described in the Cornell system, absorbed amounts were predicted of each essential AA from a diet and milk yields allowed by the most limiting AA. Regression of observed milk yield (Y) on predicted milk yield (X) using all treatment means (n = 29) was Y = 2.3 + 0.799X (r2 = 0.72). The linear relationship was stronger using 6 treatment means (n = 18) when protein supplements were fed rather than when ruminally protected AA were fed or when AA were postruminally infused (Y = -1.8 + 0.983X; r2 = 0.93). The Cornell system predicted that, for diets based on corn, Met or Lys was limiting when soybean meal was the protein source, but Lys was limiting when corn gluten meal or brewers grains were the source of protein. By AA limitation, the Cornell system explained differences in milk yield for diets that differed in supplemental protein sources in some of the experiments. As determined from milk protein yields in these studies, requirements for individual essential AA were expressed as a percentage of dietary dry matter or total essential AA, and values were relatively constant among dietary treatments and experiments.     

Influence of fat source and sorghum grain treatment on performance and digestibilities of high yielding dairy cows

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.     

Dietary variety via sweetening and voluntary feed intake of lactating dairy cows

The effects of choice of diets on feed intake were studied using 12 lactating Holstein cows. A switchback design was used that had three periods and two sequential blocks. Diets were 1) a control total mixed ration (TMR), which consisted of alfalfa haylage, corn silage, and a concentrate mixture based on ground corn and soybean meal (25:25:50 on a dry matter basis) and 2) a sweetened TMR in which a brown sugar food product constituted 1.5% of the dietary dry matter. Treatments consisted of the control TMR fed on both sides of divided feed bunks, the sweetened TMR fed on both sides of divided feed bunks, or both TMR fed on alternating (daily) sides of divided feed bunks in tie stalls. Periods were 2 wk in duration, and cows averaged 67 and 53 d of lactation at the start of blocks 1 and 2, respectively. The dry matter intake, body weight, milk yield, and percentages of milk fat, protein, and solids not fat were similar when either TMR was fed alone. A choice of control TMR or sweetened TMR did not affect any of these variables. The dry matter intake, body weight, milk yield, and milk protein percentage were affected by block; however, these effects were probably caused by differences between the blocks in environment and stage of lactation. The results of this experiment might have been affected by the composition of the control TMR, its similarity to the sweetened TMR, availability of both diets simultaneously when a choice was offered, and use of a TMR instead of separate feeds or simpler mixtures.