Fat-corrected Milk Production Research Articles

Systems to Evaluate the Protein Quality of Diets Fed to Lactating Cows

Ten multiparous and 5 primiparous cows (62±33 d in milk) were used in a replicated 5×5 Latin square design to investigate three dietary protein evaluation systems for lactating cows: milk protein score, Cornell Net Carbohydrate and Protein System, and an increase in Lys and Met to supply 15 and 5% of the predicted total essential amino acids (AA) in duodenal digesta, respectively. Five isonitrogenous diets were evaluated differently by the three systems. The milk protein score indicated that formulations of diets 2, 3, 4, and 5 were of equal quality and better for milk protein synthesis than was diet 1. The Cornell Net Carbohydrate and Protein System indicated that diets 3, 4, and 5 contained adequate AA, but diets 1 and 2 were deficient in Lys and Met. The increase in Lys and Met supply indicated that only diets 3 and 5 provided adequate Lys and Met. The dry matter intake, energy-corrected production, and fat production were lower, and 3.5% fat-corrected milk production tended to be lower, for cows consuming diets 4 and 5 than for cows consuming diets 2 and 3. Cows consuming diet 1 had lower percentages of crude protein, true protein, and casein N in their milk than did with cows consuming all other diets. Cows fed diets 3 and 5 had higher percentages of protein in milk than did cows fed other diets. Protein production was greater, and casein N tended to be greater, for cows consuming diet 3 than for cows consuming diet 2. Although all three systems had validity, the system by which Lys and Met were increased most accurately predicted milk protein percentages and production.

Effect of Calcium Soaps of Fatty Acids and Administration of Somatotropin in Early Lactation on Productive and Reproductive Performance of High Producing Dairy Cows

This study examined the mechanisms by which calcium soaps of fatty acids and bovine somatotropin (bST) affect production and reproduction of high producing cows. Calcium soaps of fatty acids were fed at 2.2% dry matter, and 500mg of Zn-sometribove (Monsanto Inc., St Louis, MO) were injected subcutaneously every 14 d from 10 to 150 d in milk (DIM).Production of fat-corrected milk was increased by 3.5 kg/d when calcium soaps of fatty acids were fed, by 6.1 kg/d when bST was administered, and by 7.4 kg/d when calcium soaps of fatty acids were fed and bST was administered. Body weight was similar for cows on all treatments until 85 DIM after which cows that were treated with bST had lower body weights. Body condition scores decreased more for cows treated with bST and began increasing later and more slowly. Treatment with bST resulted in more cows that experienced first ovulation after 30 DIM, and more cows on the control treatment exhibited first estrus before 35 DIM. Days open were greater when bST was administered. After the first artificial insemination, conception rates were similar for cows on the control treatment and for cows fed calcium soaps of fatty acids; conception rates after the first artificial insemination were low for all cows treated with bST. Pregnancy rates at 120 and 150 DIM were decreased by bST.Number of DIM to first ovulation, number of DIM to first estrus, and days open were negatively correlated with glucose and cholesterol concentrations in plasma. Production of fat-corrected milk was correlated with days open and with concentrations of triglycerides in plasma, nonesterified fatty acids, and cholesterol. Increased production had different effects on reproduction when induced by calcium soaps of fatty acids or bST treatment. Some of the adverse effects of bST treatments were alleviated by calcium soaps of fatty acids.

Efeitos da lasalocida sobre a produção de vacas leiteiras em sistema semi-intensivo

Foram estudados os efeitos da lasalocida sobre a produção de leite, teor e percentagem de gordura no leite, variações de peso e condições corporais de 18 vacas leiteras do ecótipo Mantiqueira, com média de 75 dias pós-parto ao início do experimento, alimentadas com 1,0 kg de mistura de concentrados para cada 2,5 kg de leite produzidos acima dos primeiros 4,0 kg, capim elefante (Pennisetumpurpureum, var. Napier) picado, fornecido no cocho, e pastagem de Bracharia brizantha. Utilizou-se um delineamento em blocos casualizados e os tratamentos consistiram na administração diária de 0,200 e 300 mg de lasalocida/animal. O experimento teve duração de 17 semanas, sendo as quatro primeiras destinadas ao período de adaptação. Independente da dose empregada a lasalocida não alterou significativamente a produção de leite e a produção de leite corrigida a 4% de gordura, porém o grupo tratado com 200 mg apresentou maior porcentagem de gordura no leite (P < 0,05). Os grupos tratados com 200 e 300 mg apresentaram ganhos de peso, porém não estatisticamente menores em relação aos animais controle, quando os dados foram analisados como percentagem de peso vivo. Não foi observada alteração na condição corporal dos animais.

Whole Cottonseeds or a Combination of Soybeans and Soybean Hulls in the Diets of Lactating Dairy Cows

Whole raw soybeans and soybean hulls were evaluated as a dietary replacement for whole cottonseed as determined by rumination and total chewing activity, milk fat percentage, and efficiency of 4% fat-corrected milk (FCM) production. Twenty-six Holstein dairy cows (14 multiparous; 35±12 d of lactation) were assigned randomly to one of two total mixed rations (TMR) for 15 wk. The whole cottonseed TMR and the soybean plus soybean hull TMR contained 40% of a 45:55 mixture of alfalfa and corn silages (dry matter basis) and either 15% cottonseed or 15% soybeans, 8% soybean hulls, and 0.7% sodium bicarbonate. Both TMR provided 60% of dietary neutral detergent fiber from forage. The TMR, fed twice daily, were isonitrogenous (17.5% crude protein) and equal in neutral detergent fiber (30%). The TMR had no effect on dry matter intake (24.8 kg/d). The cottonseed TMR stimulated greater rumination and total chewing activity. Although milk production was greater for cows fed the cottonseed TMR (35.7 vs. 34.1 kg/d), milk fat production was unaffected by TMR (3.72%). The efficiency of 4% FCM production was similar for cows fed the cottonseed and soybean plus soybean hull TMR (1.33), and both TMR resulted in a positive net energy balance (10.9 Mcal/d). A combination of soybeans, soybean hulls, and sodium bicarbonate was an effective alternative to whole cottonseed as measured by the efficiency of FCM production.

Alfalfa Protein Concentrate as a Less Ruminally Degradable Protein Source for High-Producing Dairy Cows

Ten multiparous Holstein cows were used in a 105-day continuous feeding trial to compare soybean meal (SBM) and alfalfa protein concentrate (APC) as supplemental protein sources for high-producing dairy cows. Dairy cows with an average milk production of 35.2 kg/day were paired and randomly assigned to one of the treatments. A double reversal design was employed With 35 days per period. The comparison between treatments was made during the last 21 days of each period. Experimental diets, containing 60% corn silage and 10% alfalfa hay, were formulated to be isonitrogenous and isoenergetic (crude protein. 15.6%; net energy tor lactation, 1.60 Mcal/kg DM). Fifty percent of dietary nitrogen was provided by test proteins. Animals were fed four times daily. Chromie oxide boluses, 50 g/day were used to estimate digestion coefficients. Ruminal protein degradability in viva (%) and in situ(%)were 56.8, 68.3 and 47.3. 35.3 for SBM and APC, respectively. Dry matter intake (kg/day) was 19.1 and 18.6 for cows fed SBM and APC. respectively. Rummal parameters cows fed SBM vs APC were, pH. 6.6 vs 6.7, ammonia nitrogen(mg/dI) 10.8 vs 6.2(p less than 0.01); total volatile fatty acids (mM), 86.3 VS 84.6(P LESS THAN 0.05), acetate (%) , 50.8 vs 64.9 (p less than 0.01); propionate dry matter , 65.3 vs 61.8; crude protein . 67.6 vs 61.1 (P less than 0.05 ) neutral detergent fiber , 51.1 vs 52.5 ; acid detergent fiber, 47.7 vs 49.0 . A slightly higher (P more than 0.05 ) amount of milk was produced by cows fed APC(28.6+_ 3.5 vs 28.2+- 3.8 kg/day). Each additional gramof undergradable intake protein provided by APC continued to a 5- gram increase in 4% fat-corrected milk production.

Effects of feeding peas to high-producing dairy cows

The effect of substituting peas for soybean and canola meals as a protein source in a high-producing dairy herd was studied in 66 Holstein cows, divided into two groups based on stage of lactation, parity, level of milk production and days in milk. Two 18.5% crude protein grain concentrate diets were formulated based on the nutrient analyses of the forages available. The control grain mix contained standard protein sources, principally soybean and canola meal (SBM\CM) while the test grain mix was formulated to contain approximately 25% field peas as the major source of protein. Both grain rations were formulated to the same nutrient specifications and balanced for undegradable protein. The duration of the trial was 6 mo during which grain feeding levels were adjusted monthly based on milk yield. For cows in early lactation, 4% fat-corrected milk yield was higher (P < 0.05) for cows fed pea based concentrates (31.3 kg d−1) than for cows fed SBM\CM supplement (29.7 kg d−1). Fat-corrected milk yield was not affected by source of protein in mid- and late-lactation cows. Fat-corrected milk production was not different (P > 0.05) for cows fed SBM\CM compared with cows fed the pea supplement when cows across all stages of lactation were included in the analyses. Milk fat percent was significantly higher (P < 0.05) for early- and mid-lactation cows fed the pea supplement. The results suggest that peas can be substituted for SBM\CM as a protein source for high-producing dairy cows. Key words: Dairy cow, pea, soybean and canola meal supplement, undegradable protein, milk production

Effect of concentrate supplementation on herbage intake and milk yield of dairy cows grazing an alpine pasture

Abstract The research was performed on a natural alpine pasture (at an average altitude of 1300 m) from June to August, with 18 Brown Swiss cows divided into three groups and fed different levels of concentrates above 12 kg 4% fat corrected milk (FCM): low (L) 1 kg per 3 kg FCM, medium (M) 1 kg per 2.5 kg FCM and high (H) 1 kg per 2 kg FCM. Herbage intake was estimated during an initial 21 day period with the n -alkanes method, by collecting daily four grab samples of faeces per day and 60 samples of herbage with the hand-plucking technique. Milk production and the fat and protein contents were recorded for the entire 3 month experimental period. The average intake of herbage (12.2 kg OM) during the 21 day period was not significantly influenced by the level of supplementary concentrates. During the entire period, the production of FCM showed an increasing trend, but without significant differences, from group L to group H, namely 15.0, 15.8 and 16.9 kg, respectively. The protein content was highest (although not significantly) with the highest level of concentrates. The possibility that the lack of a relationship between herbage consumption and concentrate level was principally due to the high herbage NDF content was discussed.

Replacing maize grain with triticale grain in lactation diets for dairy cattle and fattening diets for steers

USGEN 10 triticale was compared with maize as a feed grain in a digestibility trial, a milk production trial and a fattening trial. Apparent digestibilities were determined with eight Holstein steers, in two blocks of a balanced cross-over design. The grain component of the four diets contained triticale and maize in the ratios 100:0, 66:34, 34:66 and 0:100, respectively. Digestibility coefficients were unaffected by level of dietary triticale substitution for maize. For the milk production trial eight Holstein cows were also allocated to two blocks of four animals each and fed the four treatment diets in four consecutive periods. Cows received forage consisting of 20% lucerne hay, 15% wheat straw and 65% oat silage (dry matter basis) ad libitum and a concentrate at 0.5 kg kg −1 milk produced. The grain component of the four concentrates was the same as in the digestibility trial. Milk fat percentage and 4% fat corrected milk production per kg concentrate consumed was lower ( P < 0.05) on the dietary treatment containing only triticale grain compared to that on the treatments containing different levels of maize grain. For the fattening trial 30 steers were randomly allocated to the five dietary treatments by stratified sampling. The steers received complete diets for 100 days. The grain portion of the five fattening diets consisted of 100% maize, 75% maize: 25% triticale, 50% maize: 50% triticale, 25% maize: 75% triticale and 100% triticale. Steers on the 50% maize: 50% triticale diet tended to perform better than steers on diets containing only maize or triticale grain. Feed conversion ratio (carcass) was better ( P < 0.05) for steers on the 50% maize: 50% triticale diet than for steers on the 100% triticale diet.

Impact of Nonfiber Carbohydrate on Intake, Digestion, and Milk Production by Dairy Cows

Four concentrations of dietary nonfiber carbohydrate (42,36, 30, and 24%) were evaluated using eight multiparous Holstein cows (662kg of BW; 63 DIM) in replicated 4 × 4 Latin squares with 28-d periods. Shelled corn and soybean meal were partially replaced with wheat middlings, dried brewers grains, and soy hulls to formulate 36, 30, and 24% nonfiber carbohydrate diets. Decreasing dietary nonfiber carbohydrate decreased DMI, did not affect actual or fat-corrected milk production, increased milk fat percentage, and decreased milk protein percentage and production. Apparent total tract DM and OM digestibilities were highest for 36% and lowest for 24% nonfiber carbohydrate diets. Digestibility of NDF was lowest for the 42% nonfiber carbohydrate diet. Ruminal pH and acetate:propionate increased, and total VFA concentrations decreased, as dietary nonfiber carbohydrate decreased. Ruminal degradation of alfalfa hay DM and NDF were higher for low nonfiber carbohydrate diets. Significant depression of DMI (.9 to 1.8 kg/d) coincided with dietary nonfiber carbohydrate concentration at or below 30%. Results indicate that diets for cows producing 40 kg/ d should contain more than 30% nonfiber carbohydrate and suggest little benefit of 42 over 36% nonfiber carbohydrate diets.

Effect of a soybean hull:soy lecithin:soapstock mixture on ruminal digestion and performance of growing beef calves and lactating dairy cattle

Four experiments were conducted to evaluate the effect of a soybean hull, soy lecithin, and soapstock mixture on ruminal fiber and protein digestion, growth efficiency of beef calves, and lactational performance of dairy cattle. An initial mixing experiment determined that a 4:1 ratio (DM basis) of soy lecithin:soapstock could be added to soybean hulls at 15% (wt/wt, DM basis); this mixture had acceptable mixing and handling characteristics. Dietary addition of a mixture of 85% soybean hulls, 12% soy lecithin, and 3% soapstock (DM basis; SLS) to provide 0, 3, 5, or 7% supplemental fat resulted in a linear (P < .01) decrease in in situ rate of ruminal NDF digestion with no effect on rate of CP digestion. Daily gain, DMI, and feed efficiency (kilograms of gain/kilogram of DMI) of growing beef calves were not affected (P > .10) as graded levels of SLS replaced corn grain. However, as graded levels of SLS replaced soybean hulls, daily gain and feed efficiency increased linearly (P < .01). Based on the results of these trials, Holstein dairy cattle were fed four isonitrogenous and isoenergetic diets that contained either high levels of nonfiber carbohydrates (43%) and no added fat, 1% ruminally inert fat, a 6% level of SLS, or a 12% SLS level (all on DM basis). Efficiency of 4% fat-corrected milk production (kilograms of milk/kilogram of DMI) was greatest for cows fed SLS at 6% of dietary DM. The SLS mixture was an excellent source of fiber and vegetable fat, comparable in feeding value to corn grain, for inclusion in the diets of beef calves and dairy cows.

The Influence of Forage Type on the Production Response of Lactating Dairy Cows Supplemented with Different Types of Dietary Fat

Research has demonstrated a difference in fat utilization by lactating dairy cows with different dietary forage types. Responses appear to be greatest on alfalfa-based diets and poorest on all corn silage-based diets. The addition of extruded soybeans to dairy cow diets containing corn silage and alfalfa hay increased fat-corrected milk (FCM) production by an average of 2.4% compared to 10% for all alfalfa silage-based diets. In 11 experiments, the addition of whole cottonseed (WCS) to corn silage-based diets decreased FCM production by an average of 4% whereas the addition of WCS to alfalfa hay-based diets increased average milk fat percent and FCM production by 11 and 6%, respectively. When WCS was included in diets with corn silage as the primary forage and alfalfa hay or bermudagrass hay as a secondary forage, the fatinduced milk fat depression found on corn silagebased diets appeared to be alleviated. Alfalfa diets supplemented with yellow grease increased average milk production by 6.6% with milk fat percentage unchanged. Results supported the inclusion of tallow at 500g/cow/day in diets based on ryegrass silage whereas the inclusion of tallow or blended animal-vegetable fats on corn silage- or cottonseed hull-based diets was not supported by summarized experiments. Supplementing corn silage/alfalfa silage-based diets with prilled fat increased FCM production by an average of 6.2% whereas the inclusion of prilled fat in alfalfa silage or corn silage based diets had inconsistent effects on production responses. The supplementation of different forage-based diets with Ca-salts of fatty acids resulted in an average FCM production increase of approximately 5%.

Effects of dietary fat supplementation and recombinant bovine somatotropin on milk production, nutritional status and lipid metabolism of dairy cows

Sixty dairy cows were used to evaluate the effect on performance, metabolism and liver function of adding dietary fat during early lactation (weeks 3–15 postpartum) and injecting recombinant bovine somatotropin (rbST) over the entire lactation. Fat was added to an 18% protein concentrate that was offered in a 1:1 ratio of haylage:concentrate and fed as a total mixed ration. Corn in the control (CRT) concentrate was exchanged for either 2.5% animal fat (AFA), 2.5% Megalac™ calcium salts of fatty acids (CSFA) (ML1), 2.5% Purina CSFA (RP1) or 5% Purina CSFA (RP2). RbST treatment consisted of a subcutaneous injection of either a placebo, 10.3 mg rbST daily or 350 mg rbST every 14 d. Fat-corrected milk production was higher (P &lt; 0.05) in RP2-fed cows than CTR-fed cows and higher for cows injected with rbST daily than in those injected biweekly. Plasma-urea nitrogen and insulin concentrations were lower in RP2-fed cows than in CTR-fed cows and were also lower in rbST-injected cows than in placebo-injected cows (P &lt; 0.05). Plasma triglyceride (TG) and cholesterol concentrations, but not non-esterified fatty acid and phospholipid concentrations, were higher (P &lt; 0.05) in RP2-fed cows than in CTR-fed cows. CSFA supplementation increased C16:0 of the plasma TG fraction and decreased that of C18:0. Dietary fat supplementation did not affect hepatic lipid composition, but liver-TG concentration increased (P &lt; 0.05) with rbST injections. Dietary fat supplementation together with somatotropin injections did not change production parameters from those found with fat supplementation or somatotropin alone. Key words: Dietary fat, dairy cows, bovine somatotropin, lipids

Displaced Abomasum

Incidence of displaced abomasum (DA) in dairy cows is at least 10 times higher in Wisconsin herds than in Sweden, even though average fat-corrected milk production levels are similar. In southern Wisconsin an incidence of 2.5-3.5% appears normal (Dr. Rhoda, personal communication, Evansville, WI).&#x0D; Feed ingredient and breed differences may be associated with different incidence rates between countries. However, a preliminary investigation (Pehrson, unpublished) indicated that Wisconsin feeding and management practices during the peripartal period may be closely associated with the high incidence rate. The primary objective of the present study was to further evaluate this hypothesis (Trial B). A secondary objective was to collect clinical data with regard to occurrence of DA in the same geographic area (Trial A).

Influence of diet composition, dry-matter intake, milk production and energy balance on time of post-partum ovulation and fertility in dairy cows

AbstractLactating Holstein-Friesian cows from two calving groups (no. = 90) were studied during the early post-partum period to determine the effect of dry-matter intake (DM1), 40 g/kg fat-corrected milk (FCM) production, energy balance (EB), parity, and food additives (calcium salts of long-chain fatty acids [CaLCFA] and niacin) on the recrudescence of ovarian function and establishment of pregnancy. Cows that ovulated early during the post-partum period (15 to 21 days after calving) consumed more food and tended to produce more FCM compared with cows ovulating later (22 to 42 days or after 42 days). Primiparous cows had lower EB and tended to have longer intervals to first ovulation compared with multiparous cows but the average interval to pregnancy was similar for primiparous and multiparous cows. Feeding CaLCFA tended to extend the interval to first service and decreased pregnancy rate. Production characteristics (including DMI and FCM production) seem to determine interval from calving to first ovulation as well as interval from calving to pregnancy (days open). Fertility was affected negatively by feeding CaLCFA.

Management differences and dairy results

In representing dairy production as a function of herd management decisions, veterinarians and animal scientists have generally neglected variations in worker performance. This article presents a model that includes organization and personnel management as determinants of dairy operational results. Herd production and manager interview data from 87 farms in Tulare County, California, indicated that these management factors are related to both milk output and herd reproduction efficiency. Manager assumptions about worker motivation, regularity of employee performance feedback, and use of records explained significant variation in fat corrected milk production, somatic cell count, average days open, and services per conception. The study suggests that greater attention to organizational and personnel management could improve results of dairies as well as other agricultural businesses.

EVALUATION OF BARLEY AND WHEAT HEAD-CHOP SILAGES FOR DAIRY COWS

Head-chop silages made from barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) harvested at the mid- to late-dough stage of maturity were evaluated by laboratory methods and by feeding to dairy cows. There were linear decreases in crude protein (CP) content and in vitro true digestibility (IVTD) when comparisons of grain, heads, heads + 15 cm straw, heads + 30 cm straw and heads + 45 cm straw were made. The barley and wheat head-chop silages produced for the cow feeding trial averaged 19.9 and 22.7% ADF and were readily accepted by the cows. The head-chop silages were fed at 22 kg cow−1 d−1 (as-fed basis) plus a grain mixture according to production level. The total grain consumption was similar to that of the control cows which were fed 1 kg of grain per 3 kg of milk produced. All cows were fed timothy (Phleum pratense L.) silage ad libitum. Cows fed the wheat head-chop consumed less total feed (P &lt; 0.01) than those fed the other two treatments and produced less milk (P &lt; 0.01); but, milk fat content was higher (P &lt; 0.01) so there were no significant differences in fat corrected milk production among the treatments. It was concluded that head-chop silage was a suitable way of conserving cereal crops for feeding dairy cows. Key words: Barley, wheat, head-chop, dairy cows, silage

Feeding calcium soaps of fatty acids to lactating cows: effect on production, body condition and blood lipids.

Ca soaps of fatty acids (CSFA, 0.5 kg/d) were added to the diet of lactating cows for 170 d, and production, body condition score and blood lipids were examined. Production of fat-corrected milk was increased by 1.5 kg/d owing to increase in both milk and fat production. Over 250 d lactation, production of fat-corrected milk was enhanced by 1.3 kg/d. Body condition scores were lower in cows fed CSFA in early lactation, but tended to exceed those of control cows after 80 d lactation. Reproductive performance was improved in cows fed CSFA. Serum total lipids, phospholipids and cholesterol were increased in CSFA cows at 15 and 29 d but not at 59 d post partum. The cholesterol increase was mainly in the high density lipoprotein fraction.

EFFECTS OF FEEDING SODIUM BICARBONATE TO PREPARTUM DAIRY COWS ON THEIR PERFORMANCE IN EARLY LACTATION

Forty cows of second or greater parity were selected and blocked into 20 groups of two and randomly assigned to one of two prepartum diets; control prepartum (CP) or buffer prepartum (BP). The prepartum ration consisted of 85% grass hay, 10% ground corn and 5% dry cow supplement (dry basis). Sodium bicarbonate (NaHCO3) was fed at 0.6% of the total dry matter (DM) in the BP group. The postpartum ration was formulated to meet requirements for high-producing dairy cows in early lactation. Dry cows were placed on prepartum treatments 3 wk prior to expected calving date and abruptly switched to the postpartum ration on day 4 after parturition. For the first 4 wk of lactation the average daily total and concentrate DM intake as a percentage of body weight (BW) for cows fed rations BP and CP were not different. Forage intake as a percentage of BW and average production of 4% fat-corrected milk (FCM) was greater for CP than for BP. Milk fat test for CP and BP was not different. No differences were observed between CP and BP for rumen fluid parameters measured on days 14, 7 and 3 ± 2 prepartum. Total VFA (mg dL−1) and ratio of acetate-to-propionate was greater for CP than for BP; butyrate as a percentage of total VFA was greater for BP than for CP. Compared to controls, cows fed NaHCO3 prepartum did not perform as well during the first 4 wk postpartum as indicated by their lower forage intake and 4% FCM production. Key words: Sodium bicarbonate, cows (dairy), prepartum, performance

The interaction between dietary fibre level and protein degradability in dairy cows

ABSTRACTA trial was performed to investigate the interaction between energy and protein source for cows in negative energy balance. Six cows were assigned to each of four types of concentrate (metabolizable energy (ME) 12 MJ/kg dry matter (DM), crude protein (CP) 180 g/kg DM) with low or high fibre contents (LF or HF) and protein degradability (LD or HD). For groups HDLF, LDLF, HDHF and LDHF respectively, acid-detergent fibre contents (g/kg diet DM) were 69·2, 66·1, 117·5 and 113·3; protein degradability values were determined as 0·78, 0·61, 0·72 and 0·66. Low-fibre diets were given at the rate of 11 kg/day concentrates with 6 kg/day hay (ME 8 MJ/kg DM, CP 84·5 g/kg DM) and high-fibre diets at the rate of 10 kg/day concentrates with 7·5 kg/day hay from weeks 4 to 13 of lactation. Cows were given a standard diet over the first 3 weeks of lactation and performance in week 3 was used as a covariate.Milk yield was not affected by treatment but the butterfat content of milk from cows given the high-fibre diets (44·9 g/kg) was higher than the low-fibre diets (36·4 g/kg; P &lt; 0·01), which resulted in significant differences in fat-corrected milk yield (HDHF: 25·1, LDHF: 26·2, HDLF: 22·7, LDLF: 21·5, s.e.d. 1·5 kg/day). ME balance was lower for the LDHF group (−4·1 MJ/day) than for groups LDLF and HDLF (-15·4 and -16·8 MJ/day; P &lt; 0·05) but was not significantly different from the HDHF group (-29·4 MJ/day). Undegradable protein (UDP) balances were 53·4, 93·8, -21·2 and 193·8 (s.e.d. 45, P &lt; 005) g/day for groups HDLF, LDLF, HDHF and LDHF respectively. Differences from zero in ME and UDP balance were accounted for in all groups except LDHF by changes in live weight plus a systematic correction of approximately 10 MJ/day. It is considered that the cows given high-fibre diets responded to high UDP by increasing fat-corrected milk production but mobilization of body fat to support this increase was accompanied by retention of protein with associated water, resulting in very little change in live weight. It is also probable that the high UDP levels improved the digestion of fibre i n the rumen, but this is unlikely to have been sufficient to have accounted for all of the response.

Physiological Effects of Whole Cottonseed in Diets Fed to Dairy Cattle

Whole cottonseed (WCS) contains high concentrations of nitrogen, fiber, and net energy. The fat (oil), gossypol, and cyclopropene fatty acid (CPFA) content of WCS result in physiological effects both advantageous and deterimental to economical milk production. Little milk yield response has been observed from feeding WCS, but milk fat yield and percentage are often increased as is 4% fat-corrected milk production, while the concentrations of long chain fatty acids are increased. Milk protein content is usually decreased. Increases in plasma free fatty acids as a result of feeding dietary fat (including WCS) elicit endocrine changes, such as increased plasma insulin:glucagon ratio and insulin resistance, that may alter glucose metabolism and protein systhesis in the mammary gland and other tissues. Long term feeding of over 20 g free gossypol/d to dairy cows may result in clinical signs of gossypol toxicity. Gossypol toxicity may be a largely subclinical phenomenon in dairy cattle, reducing liver function and decreasing heat tolerance. Gossypol toxicity appears to require ingestion of 5 kg WCS/d/cow over an extended time. Health effects of dietary CPFA which are co-carcinogens with aflatoxin, are unknown. Feeding CPFA does alter lipid metabolism. Diets containing several cotton by-products should be avoided due to possible gossypol toxicity, and WCS should not be fed at over 25% of dietary dry matter, reduced to 15% during the summer months. Long-term feeding of WCS or other cotton products may be deterimental to maximum production and liver function.