Feeding In Early Lactation Research Articles

Feeding sows during the transition period-is a gestation diet, a simple transition diet, or a lactation diet the best choice?

Three experiments were carried out to study whether a gestation diet, a simple transition diet, or a lactation diet is the best choice in late gestation and when sows preferably should be transferred to a high crude protein (CP) lactation diet. In experiment 1, 35 sows were fed either a gestation diet (12.1% CP), a lactation diet (15.9% CP), or a 50/50 mix (simple transition diet; 14.0% CP) from 6 d before parturition until parturition, to study the impact on farrowing and colostrum performance. In experiment 2, 90 sows were studied from 6 d before parturition until weaning at day 24 and they were fed one of five strategies: a gestation diet until day 3 or day 10 of lactation (strategy 1 and 2) and then lactation diet; a simple transition diet until day 3 or day 10 (strategy 3 and 4) and then lactation diet; or a lactation diet throughout the study (strategy 5). In experiment 3, 124 sows were fed strategy 1 or 5. Sows were weighed and back fat (BF) scanned when entering the farrowing unit and at day 2, 10, 17, and 24. Piglets were weighed at birth and after 24 h, and colostrum production was studied (experiment 1). Litter weight at day 2, 10, 17, and 24 was recorded, milk and blood samples were collected weekly and sow fat and protein mobilization, and balances of energy, N, and Lys were calculated from day 3 to 10 of lactation (experiment 2). Total- and live born piglets, and frequencies of stillbirth and piglet diarrhea were recorded (experiment 3). Feeding sows a gestation diet, a simple transition diet, or a lactation diet showed no evidence of effects on colostrum production or farrowing process (experiments 1 and 3) or lactation performance (experiments 2 and 3). Compared to previous studies, sows had a poor milk yield. Plasma urea was elevated (P < 0.001) indicating CP oversupply prior to parturition in sows fed the lactation diet as compared with the two other diets. According to calculated balances, all dietary strategies supplied insufficient amounts of N and Lys from day 3 to 10, indicating that the best choice is to feed sows with a high CP lactation diet from parturition and onwards. Primiparous sows had a higher plasma insulin concentration (P < 0.01), lower colostrum yield (P < 0.01), and higher frequency of piglet diarrhea (P < 0.001) than multiparous sows. In conclusion, in our conditions (high CP in gestation diet; poor milk yield; restricted feeding in early lactation), sow performance was not compromised by the dietary strategies, but results indicate that primiparous and multiparous sows should be fed differently.

Effects of feeding high-quality hay with graded amounts of concentrate on feed intake, performance and blood metabolites of cows in early lactation

ABSTRACTDairy cows are commonly fed energy-dense diets with high proportions of concentrate feedstuffs to meet the increased energy needs of early lactation. However, feeding large amounts of concentrates may cause rumen acidosis and impact cow health. The hypothesis tested was that the energy supply and metabolic health of early-lactation Simmental cows can be maintained when high-quality hay rich in water-soluble carbohydrates (WSC) and crude protein (CP) is fed, despite the proportion of concentrates in the diet being reduced or even excluded. Twenty-four Simmental cows were allocated to one of four feeding groups beginning 10 d before the expected calving date, until 28 d thereafter. The feeding groups were 60CH (60% conventional fibre-rich hay plus 40% concentrate feed), 60HQH (60% high-quality hay plus 40% concentrate feed), 75HQH (75% high-quality hay plus 25% concentrate feed) and 100HQH (100% high-quality hay). The fibre-rich hay and high-quality hay differed in WSC content (110 g vs. 198 g of dry matter (DM)), neutral detergent fibre (646 g vs. 423 g of DM) and CP (65 g vs. 223 g of DM). Individual feed intake and milk production were monitored daily, and blood samples were collected weekly. Dry matter intake (DMI) and milk yield increased post partum, but 4 weeks post partum, the DMI of cows fed 100HQH only reached a daily mean DMI of 18.6 kg, whereas the DMI of the other groups averaged 21.9 kg (p < 0.046). The negative energy balance was less pronounced in cows fed 75HQH since they showed similar milk yields to the cows fed 60CH and 100HQH, but their energy intake was higher. Concentrations of milk components were similar across rations 60CH, 60HQH and 75HQH, as were most of blood parameters. Cows fed 100HQH responded to the energy deficit post partum with a higher ratio of non-esterified fatty acids to cholesterol and a higher concentration of ß-hydroxybutyrate (significant in comparison to cows fed 75HQH, p < 0.05). In conclusion, feeding high-quality hay with a WSC content of 20% in DM has the potential to decrease the proportion of concentrates in dairy cow feeding in early lactation, but cannot fully replace their supplementation due to a limited rumen capacity for forage intake.

1323 Effect of early lactation feeding strategy on production, metabolic and endocrine responses of primiparous dairy cows

1323 Effect of early lactation feeding strategy on production, metabolic and endocrine responses of primiparous dairy cows

Invited review: Carryover effects of early lactation feeding on total lactation performance in dairy cows

In comparison with the intensive research on the direct effects of energy supply on dairy cow lactation performance, little attention has been paid to the effect of early lactation feeding on subsequent production. The present paper reviews 9 studies carried out with the aim of quantifying the immediate and subsequent responses in milk production and body weight to early lactation feeding. Most results showed that a more generous feeding in early lactation caused a positive carryover effect on subsequent production, whereas an inadequate level of feed in early lactation has been shown to reduce subsequent milk yield. The carryover periods ranged from 3 to 12 wk and the difference in milk yield between cows in the carryover periods ranged between 1.5 and 4.5kg of milk/cow per day. When calculated as a percentage of the immediate effect, the carryover effect ranged from 22 to 63%. In 2 of the 9 papers reviewed, the authors found no carryover effect, probably due to the long post-treatment periods in these studies. This is supported by the other studies in which the carryover effect was only significant in a limited period after end of treatment. The magnitude of the carryover effect seems to be determined by several factors including duration of the treatment and post-treatment feeding level. The most important factor though appears to be the magnitude of over- or underfeeding (i.e., a strong relationship between the treatment period feeding level and the subsequent response in production).

Effects of supplemental chromium propionate and rumen-protected amino acids on productivity, diet digestibility, and energy balance of peak-lactation dairy cattle

Chromium (Cr) feeding in early lactation increased milk production in some studies, but responses to dietary Cr during peak lactation have not been evaluated. Furthermore, interactions of essential amino acids (AA) and Cr have not been explored. Our objective was to evaluate responses to CrPr (KemTRACE chromium propionate 0.04%, Kemin Industries Inc., Des Moines, IA) and rumen-protected Lys (LysiPEARL, Kemin Industries Inc.) and Met (MetiPEARL, Kemin Industries Inc.) and their interaction in peak-lactation cows. Forty-eight individually fed Holstein cows (21 primiparous, 27 multiparous, 38±15d in milk) were stratified by calving date in 12 blocks and randomly assigned to 1 of 4 treatments within block. Treatments were control, CrPr (8mg/d of Cr), RPLM (10g/d of Lys and 5g/d of Met, intestinally available), or CrPr plus RPLM. Treatments were premixed with ground corn and top-dressed at 200g/d for 35d. Diets consisted of corn silage, alfalfa hay, and concentrates, providing approximately 17% crude protein, 31% neutral detergent fiber, and 40% nonfiber carbohydrates. Dry matter intake (DMI) significantly increased with the inclusion of CrPr (22.2 vs. 20.8±0.67kg/d), and energy-corrected milk (ECM) yield tended to increase. In addition, CrPr increased milk protein yield and tended to increase DMI in primiparous cows but not in multiparous cows. A CrPr×week interaction was detected for milk lactose content, which was increased by CrPr during wk 1 only (4.99 vs. 4.88±0.036%). As a proportion of plasma AA, lysine increased and methionine tended to increase in response to RPLM, but the inclusion of RPLM decreased N efficiency (milk protein N:N intake). Digestible energy intake, gross energy digestibility, and energy balance were not affected by treatments. We observed no treatment effects on feed efficiency or changes in body weight or body condition score. In summary, feeding CrPr increased DMI and tended to increase ECM in cows fed for 5wk near peak lactation, with primiparous cows showing greater responses in DMI and milk protein yield than multiparous cows.

Partial replacement of corn grain with calcium salts of fatty acid in the concentrate fed to grazing primiparous and multiparous dairy cows

The effects of the partial replacement of corn grain with calcium salts of unsaturated fatty acids (CSFA) on milk yield and composition, milk‐fatty acid profile and parameters linked to body lipid mobilisation were examined in 32 multiparous (MC) and 18 primiparous (PC) grazing cows in early lactation. Cows grazed a lucerne pasture and received a concentrate composed (DM basis) of 4.5 kg day‐1 of ground corn grain and 0.4 kg day‐1 of fish meal (Control) or similar to Control but replacing 1.8 kg of corn grain with 0.8 kg of CSFA (Fat). Pasture (14.3 kg cow‐1 day‐1), total dry matter intake (18.5 kg cow‐1 day‐1) and total energy intake (32.6 Meal NEL (net energy of lactation) cow‐1 day‐1) were not affected by dietary treatments or parity. Total energy consumed from the concentrates averaged 10.4 Meal NEL cow‐1 day‐1. Milk yield was increased in Fat on PC (20.4 versus 22.2 kg day‐1) but no effects were detected on MC. Milkfat concentration was reduced (‐2.4 g kg‐1) by Fat (P < 0.02). Fat‐corrected milk (24.5 versus 21.2 kg day‐1) and milkfat yields (0.93 versus 0.76 kg day‐1) were decreased by feeding CSFA on MC, with no effects on PC. Milk protein content was increased (31.9 versus 33.0 g kg‐1) in MC but decreased (32 versus 30.9 g kg‐1) in PC by CSFA. The lower fat‐corrected milk and milkfat yields in MC fed Fat lead to a higher (P < 0.05) estimated energy balance (6.27 Meal NEL day‐1) compared to Control (1.11 Meal NEL day‐1) cows, but changes in body weight gain (0.03–0.11 kg cow‐1 day‐1) were not detected. In PC, body weight was reduced (‐0.185 kg cow‐1 day‐1) and this affect was not reduced by feeding unsaturated CSFA. Plasma concentration of non‐esterified fatty acids was higher in PC than MC and not affected by CSFA either before (basal) or after the injection of a lipolytic agent (isoproterenol). Plasma concentration of glucose, urea and triglycerides were not affected by treatment or parity. Plasma cholesterol concentration was similar between PC and MC cows and higher in CSFA treatments. Concentration of de novo syn‐thesised fatty acids (C4.0 to C14.1) were decreased and that of unsaturated long chain FA (C18:1, C18:2 and C18:3) was increased by supplemental CSFA. Milkfat content of conjugated linoleic acid (cis‐9, trans‐11, CLA) was increased (+0.23 g 100 g‐1) by CSFA only in MC. The partial replacement of corn grain by unsaturated CSFA depressed fat‐corrected milk yield and improved the estimated energy balance in MC without changes in parameters linked to body lipid mobilisation. The health value of the milk for the consumer was improved through a reduction in the hypercholesterolemic fraction of milkfat and the increase in milk CLA content. PC responded to unsaturated fat feeding through an increase in milk production without changes in fat‐corrected milk. Supplemental fat did not reduce parameters linked to body lipid mobilisation. More studies are needed involving grazing PC to better understand the potential benefits of unsaturated fat feeding in early lactation.

Effects of level of feeding of concentrates during early lactation on the yield and composition of milk from grazing dairy cows with varying body condition score at calving

An experiment was undertaken to establish the influence of body condition at calving on milk production and composition using diets typical of those currently used in Victoria. Seventy-two cows were fed differently from April 2001 to achieve target body condition scores (BCS) by 1 month before calving of about 4�(3.5–4.5), 5 (4.5–5.5) or 6 (5.5–6.5) units on an 8-point scale. The actual mean BCS at calving for the 3 treatments were 3.8, 5.2 and 5.7 units (P&lt;0.05). After calving, cows grazed at pasture allowances of about 35 kg DM/cow.day and received 1 of 2 levels of supplementation (1 or 6 kg DM of pelleted concentrates per day) for about the first 10�weeks of lactation. The low BCS cows lost less body condition (0.35 v. 1.27 units; P&lt;0.05) for a shorter period (4.8 v. 7.9 weeks; P&lt;0.05) than did the medium and high BCS cows. The low BCS cows also ate more pasture than the other 2 BCS groups, but only when expressed as a percentage of liveweight (2.91 v. 2.73%; P&lt;0.05). Improvements in BCS at calving resulted in higher milk fat percentages in early lactation (3.31% for low BCS cows v. 3.60% for the 2 higher BCS groups; P&lt;0.05), while milk protein and lactose were not affected (P&gt;0.05). At the lower level of feeding in early lactation, milk production increased (P&lt;0.05) linearly as BCS at calving increased, by 1.0 kg milk per unit of body condition per day. However, when energy intake was increased by feeding 6 kg of concentrates, milk production increased as body condition increased (P&lt;0.05) from the low to medium BCS, but there was no significant benefit beyond the medium BCS. Therefore, the hypothesis, that providing that cows are fed well with grazed pasture supplemented with high-energy concentrates in early lactation, BCS at calving will have no effect on subsequent milk production, was at least partially disproved, and it may be that it is never possible for cows at pasture to be sufficiently well fed.

Changes to the amounts of compounds for mid lactation cows as a method of modifying milk output

The application of milk quotas has stressed the importance of maximising the financial margin per litre of quota as well as those margins calculated on a per cow or a per hectare basis. Since quotas were Introduced there has been a move towards exploiting the value of high quality forage by reducing the amounts of compound feed supplementation. However, low amounts of compound feeding in early lactation can cause ketosis or can reduce fertility. So many farmers with autumn calving cows have tended to feed high amounts of compounds for the first three months of lactation and then, about the end of the calendar year, decide whether changes in feeding are necessary to meet quota targets for the last quarter of the year.

Subclinical Ketosis in Dairy Cows

Subclinical ketosis is defined as a preclinical stage of ketosis. The peak prevalence of subclinical ketosis occurs during the fourth week of lactation. Herd-related factors, breed, parity, and season are other important determinants. Subclinical ketosis can be revealed by determining levels of plasma glucose, plasma NEFA and blood, and milk or urine ketone body concentration. There are theoretical and practical advantages of using milk ketone bodies. Most authors are agreed on approximate lower and upper borderlines for subclinical ketosis. The risk of an outbreak of clinical symptoms has been evaluated by some authors. Most authors have found significant negative relationships between energy balance and ketone body concentration. Some disagreement may be attributable to the fact that the diets used in different experiments can have different glucogenic potential, even if the energy content is the same. This affects the relationship between energy balance and ketone body concentration, as the ketone body level is influenced by both the energy balance and plasma glucose. Feeding silage with high butyric acid content increases the risk of subclinical ketosis. There are indications that cows with the highest milk yield directly after calving are at greatest risk for developing ketosis. Increased ketone body level secondarily reduces milk production, a decrease that has been quantified by some authors. Subclinical ketosis causes delayed reproductive functions return to normal after calving, increased intervals from calving to first and last service, and an increased frequency of ovarian cysts. The routine determination of milk acetone levels in control programs can be used to evaluate the status of individual cows, to indicate the energy feeding in early lactation at a herd level, and to evaluate sires for breeding. The heritability and the tendency toward a positive genetic correlation between milk acetone and milk yield have also been discussed, as have aspects of nutritional prevention. Factors such as energy- and protein-rich roughage, tasty high-energy concentrates, suitable feeding during the dry period, and division of the concentrates into at least four meals are considered to be important.

Nutrition and reproductive performance of dairy cattle 1. The effect of level of feeding in late pregnancy and around the time of insemination on the reproductive performance of first lactation dairy heifers

ABSTRACTOne hundred first lactation Friesian dairy heifers were used to investigate the effect of level of nutrition n i late pregnancy and for a limited period around the time of insemination on reproductive performance. The heifers were housed throughout the period of the trial in cubicle yards and all individuals were given controlled amounts of food.Fifty animals were offered a ‘high’ (H) level of feeding in late pregnancy (for 10 weeks before calving) and 50 were offered a ‘low’ (L) level. After calving, the heifers were re-randomized with half of each pre-calving group being offered either the H or L level of feeding in early lactation (weeks 6 to 18), thus forming four subgroups of 25 heifers: HH, HL, LH and LL. The level of feeding in late pregnancy for all groups increased towards calving. The high plane heifers consumed 83·6 MJ metabolizable energy (ME) per day on average compared with 64·6 MJ ME per day for the low plane heifers, a proportional mean difference of 0·29 (P &lt; 0·001). After calving, heifers consumed an average of 86 MJ ME per day in week 1 rising to 126 MJ ME per day by week 5. Between weeks 6 to 18 of lactation, the high plane group consumed an average of 146·8 MJ ME per day compared with 119·8 MJ ME per day for the low plane group, a proportional mean difference of 0·23 (P &lt; 0001).There were no significant effects of feeding treatments on milk yield. Fat yield in weeks 6 to 18 was increased by the high level of feeding in lactation (P &lt; 0001), while protein yields in weeks 1 to 5 and n i weeks 6 to 18 were increased by high plane feeding in pregnancy (P &lt; 0·05) and lactation (P &lt; 0·05), respectively. Heifers receiving the high level of feeding in late pregnancy gained significantly (P &lt; 0·001) more weight than those on the lower level of feeding. All groups lost similar amounts of weight during the first 5 weeks after calving, but there were marked differences in the rate of live-weight gain between weeks 6 to 11 of lactation (P &lt; 0·05 to P &lt; 0·001). In particular, the HL group had the lowest rate of live-weight gain, and this was significantly lower than that of the HH group (P &lt; 0·01).First ovulation occurred significantly earlier in heifers receiving the high level of feeding in pregnancy P ( &lt; 0·01), but there was no effect of treatment on ovulation detection rate, time to first oestrus, time of first insemination or the proportion of wrongly-timed inseminations. Heifers receiving the high level of feeding in lactation had a successful pregnancy rate to first insemination of 0·42 compared with 0·63 for those on the lower level of feeding (P &lt; 0·05), with the greatest difference observed between the HL group (0·72) compared with the HH group (0·35) (P &lt; 0·01). Embryo loss rate was low in the HL group (008) compared with that in the HH group (0·26; P &lt; 0·l). The net result was that the HH group had a median interval from calving to successful pregnancy of 95 days with an interquartile range of 82 days, whereas the figures for the HL group were 75 and 23 days (P &lt; 0·001). Live-weight change at artificial insemination (AI) and level and change in milk yield at AI had independent effects on reproductive performance and as a consequence net energy output showed the strongest relationship with days to successful pregnancy. Heifers with the highest net energy outputs per day at AI had the longest intervals to successful pregnancy (r = 0·408; P &lt; 0·001).

Nutritional needs of sheep in the hills and uplands

AbstractCurrent knowledge of the potential nutrient supply that can be derived from indigenous and sown pasture is described and related to classically derived nutrient requirements. From this information, nutrient deficits can be identified for specific times in the ewe's cycle of production. Whilst nutrient deficits have been clearly identified in late pregnancy and early lactation, responses to nutrients and nutrient supply from autumn pasture have not yet been adequately described for the ewe over the mating period.Nutrient deficits can be met by a combination of tissue catabolism and the provision of supplementary feeding. The dearth of knowledge of the factors influencing tissue catabolism and of the effects of supplementary feeding on herbage intake limits quantification of the amount and type of supplementary feeding to offer.The principles concerning supplementary feeding in late pregnancy in some circumstances still require elucidation because of the interactions between mid- and late-pregnancy nutrition and this will be illustrated with reference to sheep grazing a predominantly heather hill. However, the principles governing supplementary feeding in early lactation are relatively well understood in relation to sown pastures below 4 cm in sward surface height and these are outlined. Information on the relative importance of milk and herbage in the diet of the lamb to weaning is discussed. The dependence of one part of the annual cycle on the nutrition in other parts of the cycle is stressed.

The effect of feeding in early lactation on feed intake, yields of milk, fat and protein and on live-weight change over one lactation cycle in dairy cows

SummaryAn experiment has been made to study the effect of level of feeding in early lactation on the feed intake, yields of milk, fat and protein and on live-weight change over one lactation cycle. Adult British Friesian cows of high potential yield were randomly allocated to high (HP) or moderate (MP) levels of feeding for 20 weeks. They were then randomly allocated within treatments to controlled or ad libitum levels of feeding for the rest of the lactation.There were significant effects of feeding in the early part of lactation on the yields of milk, protein and lactose but not on milk fat or live-weight change. Cows on the MP treatment produced about 450 kg milk from body energy reserves but were unable to supplement fully the dietary energy deficiency. There was no significant response to feeding ad libitum in the second part of lactation and the differences in yields established in the first part were maintained in the second. There was no relationship between feed intake and milk yield for cows fed ad libitum nor did the level of feeding in early lactation influence the level of intake in the later part.There was little agreement between calculated energy balance and the live-weight changes but there was more between live-weight change and condition score.

Effect of body condition at calving and level of feeding in early lactation on milk production of dairy cows

Two experiments were carried out to measure effects of body condition at calving and different levels of feeding after calving on milk and subsequent reproduction.In experiment 1, which was conducted in two consecutive years, 162 cows (77 in year 1 and 85 in year 2) were group feed so as to reach a target body condition (condition scores ranging from 3-6) four weeks before calving. During the last four weeks before calving, all cows were managed so as to maintain their individual condition scores. At calving, cows in similar condition of similar breed and with similar previous milk production were allocated to high and low levels of feeding at pasture for the first five weeks of lactation. Mean pasture intakes were 13.0 and 7.0kg dry matter (DM)/cow.d in year 1 and 15.0 and 8.5 kg DM/cow.d in year 2In experiment 2, 40 cows were offered pasture and hay from 20 weeks before calving to achieve a body condition score of either 4 or 6 by two weeks before calving. During the first five weeks of lactation, cows were individually fed in stalls on freshly cut pasture at one of three levels of intake, 7 or 10 kg DM/cow.d or .In both experiments cows were grazed as one group from week 6 to 20 of lactation.Improved body condition at calving resulted in an extra 4.0, 11.0 and 7.4 kg milk fat per unit condition score over 20 weeks of lactation, for year 1 and 2 of experiment 1, and experiment 2, respectively. Cows in poorer condition partitioned a higher proportion of feed energy to liveweight at the expense of milk production than did the cows in better condition. However, increasing the plane of nutrition in early lactation resulted in higher levels of milk production and reduced the need for cows to mobilize bodyreserves. Improved body condition at calving had a positive effect on milk fat percentage, particularly in early lactation, but did not affect milk protein percentage. Input-output relations calculated from the experimental data showed that the benefit sf to improve body condition before calving was less than that of additional feeding after calvin changes in the condition of the cows were taken into consideration (25.8 vs 1 4.6 kg DM to yi kilogram of milkfat). Improvements in condition and feeding in early lactation reduced the anoestrus interval after calving by 5.7 d for each additional condition score at calving and 1. d for each additional kgDM/cow.d fed over weeks 1-5 of lactation. The input-output relations resented will enable farmers to assess the likely consequenes of changes in their feeding management in the crucial peripartum period with a greater degree of confidence than in the past.

The effect of different levels of nutrition at two stages of the lactation on milk production and live-weight change in Friesian cows and heifers

SUMMARYOver the 4 years 1965–8, a total of 105 mature Friesian cows and 84 Friesian heifers were fed various levels of nutrition at two stages of the lactation to study the effect on milk production. The experiments were carried out over a whole lactation at four Experimental Husbandry Farms, Boxworth, Bridget's, Great House and Trawsgoed. There were three treatment levels in early lactation (weeks 3–10) comprising 5·9, 7·8 or 9·8 kg D.M./day of concentrates for mature cows and 1·6 kg D.M./day less at each level for the heifers. In mid-lactation (weeks 12–18) the two lower levels of concentrates were fed arranged factorially with early-lactation levels. A basal forage ration usually of hay was fed to provide 85% of the basal maintenance requirements. During the remainder of the lactation all animals received the same level of nutrition. In addition to the pre-determined feed treatments, one further group of animals in each block was fed according to the milk production in the preceding week.Overall an increase in level of nutrition in early lactation produced a regular increase in milk production from successive increments with adult cows but only for the first increment with heifers. Raising feed level in mid-lactation increased milk production for all animals. There were considerable residual effects from early-lactation feeding but these were less with mid-lactation feeding. These same effects were also noted with yields of solids-not-fat and to a less extent in milk fat production.The experimental results indicated not only the mean effects of treatments but more important the interaction with individual animals. Study of the response of individual animals indicated that the effects of level of feeding varied in proportion to the potential of the cow. The presentation of mean results can therefore be misleading. The potential of a cow was indicated by milk production in the immediate post-calving period. This period could be used both in experimental designs for selecting animals in the allocation to experimental treatments and also in the practical context for rationing individuals or groups of cattle.The absolute plane of nutrition related to the potential of the animal was the most important factor in determining the efficiency of utilization of feed for milk production.

MAXIMIZING MILK PRODUCTION FROM PASTURE

Major factors influencing dairy production from pasture are briefly reviewed. Emphasis is on the results of New Zealand research on nutrition and management. Stocking rate, cow quality, liveweight' or condition at calving, level of feeding in early lactation, and nutritive value of pasture are considered to be important, but not grazing management during lactation. Limited evidence indicates that, in most instances, supplementary feeding during lactation is not economic. Modifications of management that are required as stocking rate increases are briefly discussed.

Experiments on the nutrition of the dairy heifer:IX. Food utilization in lactation

SUMMARYFood utilization by lactating dairy cows was studied in a randomized experiment covering the first 24 weeks of lactation, with further observations on performance over the remainder of the lactation under farm conditions. Over a 3-year period 90 firstcalf cows each took part in the experiment for one lactation, making six groups of 14–16 animals.For the experimental period a fixed basal diet was given of hay, concentrates, and wet brewer's grains. One group received only the basal ration. Four groups received in addition a fixed concentrates supplement for 4, 8, 12, 16 weeks from calving onwards respectively. The sixth group also had supplementary concentrates for 16 weeks but for weeks 5–12 inclusive the amount was doubled so that this group's diet simulated broadly ad libitum feeding in early lactation.Milk yield was increased by extra concentrates. The greater part of the effect was apparent in the first 2 weeks of different levels of intake, with a further build-up over the next 6–8 weeks. The size of the response fell as time from calving to initiation of different intakes increased. Additional food increased and delayed peak yield level. Persistency of milk yield was not affected by fixed differences in intake. Rate of liveweight change was improved by extra concentrates, less so in the third compared with the first month on treatment.A higher level of feeding in early lactation led to a greater partition of nutrients in mid-lactation to milk at the expense of gains in body reserves. This advantage to milk production extended to the end of lactation. In it the greatest response per unit concentrates was obtained from supplementation in the first 4 weeks of lactation but the total effect was increased by giving a double allowance of concentrates, and by extending the period of extra feeding to 8 weeks after calving.Solids-not-fat content and yield, and fat yield but not fat content, showed a similar response pattern to milk yield.Animal-to-animal variation in output on constant diets was characterized by negative regressions of live-weight change on milk yield. The regression coefficients were greater in early than in mid-lactation but they were constant in size at any one time for the various groups. A change in ration induced a change in output of the individual in which that production pathway favoured naturally by the animal was the more affected.

Effects of stocking rate and energy supplementation on milk production from tropical grass-legume pasture

Forty Friesian cows were grazed continuously on a green panic (Panicum maximum var. trichoglume)/glycine (Glycine wightii cv. Tinaroo) pasture at stocking rates of 1.3, 1.6, 1.9 and 2.5 cows ha-1 for two years on the Atherton Tableland, Queensland. A supplement of 3.6 kg crushed maize cow-1 day-1 was fed for 50 days post-partum to half the cows in each group in both years. Milk yield per cow was reduced from 3811 kg lactation-1 at 1.3 cows ha-l to 3289 kg lactation-1 at 2.5 cows ha-1. With increasing stocking rate milk yield per hectare increased linearly to 8309 kg ha-1 at 2.5 cows ha-1. At 1.9 and 2.5 cows ha-1 cows lost weight over the two years and in late lactation levels of milk solids were often low. Also at these stocking rates cows had to be supplemented for up to 60 days during the main dry season. Legume content of the pasture declined linearly (P &lt; 0.05) with increasing stocking rates. Maize feeding in early lactation increased milk yield over the total lactation by approximately 12 per cent, the response being 2.3 kg milk per kg maize fed, Response was greater at lighter stocking rates as cows in the heavier stocking rate treatments dried off prematurely. It was concluded that per hectare milk production from tropical grass/legume pastures can approach that from temperate pastures and that energy supplementation early in lactation would substantially increase per cow production.

Experiments on the nutrition of the dairy heifer: VIII. Effect on milk production of level of feeding at two stages of the lactation

SUMMARYEighty Friesian heifers were used to study the effect on milk production of two fixed levels of intake at two stages of the lactation. The rations were estimated to contain 7·9 and 6·2 kg starch equivalent per day, with adequate protein content. The heifers were allocated at random to these two levels of intake for weeks 1·9 of lactation and re-allocated at random to them for weeks 10–18 of lactation. Apart from minor variation the heifers were all fed alike for the remainder of the lactation.The higher level of feeding increased yields of milk and milk solids and solids-not-fat content in each period but had a smaller effect in mid- than in early lactation, a trend which was shown to continue further into later lactation. It also conserved body reserves.There was a residual effect in weeks 10–18 from the level of feeding in weeks 1–9 of lactation. This was directly additive to the effects of the current level of feeding. Those animals which had received the higher level of feeding in weeks 1–9 yielded more milk of higher solids-not-fat content than those which had had the lower level of feeding in weeks 1–9. The former group gained less live weight. The effect on milk production over the full lactation from additional feeding in early lactation was three times that observed in early lactation itself. Additional feeding in mid-lactation did not have a residual effect.The absolute output of milk per unit of food over the 18-week period was greatest for that group which had received the lower level of feeding throughout, followed by the group which received the higher level of feeding in weeks 1–9 only. This superiority was achieved at the expense of body reserves. There was a negative regression of live-weight change on milk production.Estimated intakes of metabolizable energy agreed closely with requirements for milk production as indicated by the Agricultural Research Council (1965).