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1.
Eight pregnant heifers (primiparous cows) and seven pregnant cows in their second, third and forth pregnancies (multiparous cows) were assigned to two groups and fed either a low calcium (Ca) diet (Ca, 0.46%) or a high Ca diet (Ca, 0.86%) ad libitum from 3 weeks before the expected calving date to 3 days after parturition. All cows were examined for a change in dry matter intake (DMI), plasma minerals and bone turnover around parturition. The dietary Ca level did not affect the DMI in both primiparous and multiparous cows. The DMI of primiparous cows was significantly lower than that of multiparous cows (P < 0.05) in both the low and high dietary Ca groups. The dietary Ca level did not affect the concentrations of plasma Ca, phosphorus, magnesium and parathyroid hormone throughout the experimental period. Plasma phosphorus in primiparous cows was significantly higher (P < 0.05) than that of multiparous cows around parturition. Plasma Ca and magnesium tended to be higher (P < 0.10) in primiparous cows. The dietary Ca level did not affect the plasma osteocalcin (OC) level measured as bone formation or the urinary deoxypyridinoline (DPD) excretion measured as bone resorption before parturition in both primiparous and multiparous cows. After parturition, the plasma OC level was lower than it was before parturition in multiparous cows fed a low Ca diet, and in primiparous cows. There were no significant differences in urinary DPD excretion between each group before and after parturition. Both the plasma OC level and urinary DPD excretion of primiparous cows were significantly higher than those of multiparous cows in both the low and high dietary Ca groups.  相似文献   

2.
Data from 65 cows were collected to clarify the relationship between parity and mineral status in Holstein cows during the periparturient period. Milk fever occurred in a second‐ and a fourth‐lactation cow at parturition. Bodyweight of cows decreased immediately after parturition, and the decreased weights of cows from 1 to 6 days after parturition ranged from 11 to 27 kg. Milk yield of multiparous cows was higher than that of primiparous cows, but Ca and P concentrations in colostrum were not affected by the parity. Plasma glucose of primiparous cows was higher than that of multiparous cows, and plasma nonesterified fatty acids of fourth‐and‐more‐lactation cows at parturition was highest. Plasma Ca concentration of cows at parturition decreased with advancing parity, and plasma inorganic P concentration of third‐and‐more‐lactation cows was lowest at parturition. Plasma parathyroid hormone of fourth‐and‐more‐lactation cows at parturition was highest, but plasma hydroxyproline and alkaline phosphatase was lowest. These results suggest that the large transfer of Ca and P to colostrum is a factor in the development of milk fever in third‐and‐more‐lactation cows.  相似文献   

3.
Eleven primiparous Holstein Friesian and their crossbred calves (F1, Japanese Black cattle × Holstein Friesian) and 10 multiparous Holstein Friesian and their Holstein Friesian calves were used to evaluate vitamin E status in periparturient period. Plasma α‐tocopherol (α‐toc) concentrations of the multiparous cows were significantly higher than those of the primiparous cows from 60 days before expected calving to 90 days of lactation (P < 0.05). The multiparous cows had a further decrease in the concentrations of α‐toc and total lipid in plasma to the calving than the primiparous cows. Colostrum α‐toc concentrations in multiparous cows were significantly higher than those of the primiparous cows (P < 0.05). Plasma α‐toc concentrations of calves borne by the multiparous cows were significantly higher than those of the primiparous cows at 5 days of age (P < 0.05). Plasma α‐toc concentrations of calves were highest at 5 and 15 days of age in the calves borne by the multiparous and primiparous cows, respectively, and decreased thereafter till 90 days of age. The higher vitamin E status of multiparous cows over primiparous cows might have reflected nutritional composition in the rations. Their calves afforded higher plasma α‐toc levels after birth because of more α‐toc transfer via placenta and more α‐toc secretion in the colostrums thereafter. Plasma α‐toc concentrations of the calves might have decreased as the calves became dependent upon the solid feed of low vitamin E content.  相似文献   

4.
The aim of this study was to investigate the relationship between the first ovulation within 3 weeks postpartum and subsequent ovarian cycles and fertility in high producing dairy cattle in Hokkaido, Japan. In Experiment 1, 110 cows (44 primiparous and 66 multiparous) were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent ovarian cycles. Milk samples were collected twice weekly from 7 to 100 days postpartum. The first ovulation was identified by an increase in milk progesterone (P4) to more than 1 ng/ml within 3 weeks postpartum. The numbers of cows showing ovulation and anovulation within 3 weeks postpartum were 31 (70.5%) and 13 (29.5%) in the primiparous cows and 35 (53.0%) and 31 (47.0%) in the multiparous cows, respectively. The patterns of ovarian resumption after calving were classified into two types (normal ovarian cycles and abnormal ovarian cycles) on the basis of milk P4 concentrations. Initiation of normal ovarian function in cows ovulated within 3 weeks postpartum occurred earlier than in anovulated cows regardless of the number of calvings (primiparous, 27.8 days vs. 44.4 days; multiparous, 30.6 days vs. 55.7 days; P<0.01). Out of the multiparous cows that ovulated within 3 weeks postpartum, initiation of normal ovarian function followed by a normal luteal phase was earlier than when it was followed by an abnormal luteal phase (25.5 days vs. 40.4 days; P<0.05). Milk P4 concentrations after the first ovulation were lower than those after the second ovulation in both the primiparous and multiparous cows (P<0.05). In Experiment 2, 22 multiparous cows were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent fertility. Blood samples were collected once a week from 0 to 3 weeks postpartum. The interval from parturition to first service in ovulated cows was shorter than in anovulated cows (68.4 days vs. 94.8 days; P<0.05). The conception rate by 100 days after calving tended to be higher in ovulated cows than in anovulated cows (50.0% vs. 16.7%, P=0.09). In conclusion, our data strongly suggests that ovulation within 3 weeks postpartum is a crucial phenomenon for subsequent resumption of ovarian function and conception, and thus it can be used as an index of subsequent reproductive performance.  相似文献   

5.
Vitamins with antioxidative functions are commonly used as supplements to improve fertility in dairy cows. However, according to field test results uncertainty exists about the effect of these vitamins, especially in vitamin A and vitamin E, on ovarian functional activity. This study was performed to reveal the physiological characteristics of cows receiving enough feed and the ovaries of which were activated in the early postpartum period. Six of 12 primiparous cows showing the corpus luteum on 25 to 27 days after parturition were classified as early responders (PER); the remaining six were classified as late responders (PLR). Among 11 multiparous cows, nine were early responders (MER), and the remaining two were late responders (MLR). Plasma concentration of thiobarbituric acid reactive substances (TBARS) in the PER were lower than those in the PLR (P < 0.01). The ratio of plasma all‐trans‐retinol to intake α‐tocopherol or β‐carotene were increased in the following order: MER < PER < PLR (P < 0.01). The milk lactose (P < 0.025) and plasma glucose (P < 0.01) of the early responders tended to be lower than those of the late responders. These may have been associated with the availability of vitamins or energy balance. Thus, we suggest the possibility that the cows which were able to utilize antioxidants and energy from the feed efficiently may have earlier resumption of ovaries postpartum.  相似文献   

6.
To estimate the relationship between heat stress during the last 60 days prepartum, body condition score and certain reproductive traits in the subsequent lactation of Holstein cows, 564 multiparous cows and 290 primiparous cows from four dairy herds were used in a hot, humid region. Maximum prepartum degree days were estimated to quantify the degree of heat stress. Multiple regressions analyses and logistic regression analysis were performed to determine the effect of prepartum heat stress and body condition change on reproductive parameters, which were obtained from DHIA forms at the end of the lactation. Multiparous and primiparous cows which gained body condition score from calving to 60 d postpartum exhibited 28 and 27 fewer days open (P?<?0.05), respectively, than cows not gaining. There was no effect (P?>?0.05) of heat stress measurement on days open or services per conception in either multiparous or primiparous cows. During hotter months of calving, multiparous cows showed higher services per conception and primiparous cows showed higher days open and services per conception (P?<?0.05). Maximum prepartum degree-days were positively associated (P?<?0.05) with calving difficulty score. Multiparous cows with high body condition score at calving were 1.47 times more likely to present a very difficult calving than cows that calved in October (P?<?0.05). Collectively, these results suggest that reproductive performance was not affected by cumulative prepartum heat stress although it was associated with very difficult calving score.  相似文献   

7.
将年龄、胎次相同，年产奶量大于7000kg的围产期荷斯坦奶牛30头随机分为3组，每组10头，低能量组（Ⅰ组）按中国奶牛营养标准2000年版减少20％日粮（能量摄入80％），高能量组（Ⅱ组）则按此标准增加20％日粮（能量摄入120％），对照组（Ⅲ组）按标准日粮（能量摄入100％）饲喂，试验从产前28d到产后56d结束，分娩后各组均按标准配制相同的泌乳日粮。分别于产前28、14d及产后1、14、28、56d采取肝活体组织。应用内对照RT—PCR方法检测肝脏组织MTPmRNA丰度。结果显示，各组奶牛肝MTPmRNA丰度均呈现先升高后降低的趋势。产后均高于产前，且产后1～28d差异显著（P〈0．01或P〈0．05），而后回降，至56d趋于平稳（P〉0．05）；Ⅲ组肝MTP mRNA丰度在产后1d达到峰值，而Ⅰ组和Ⅱ组在产后14d达到最大值（P〈0．01）；Ⅱ组产后1～28d显著高于I组。产后14d显著高于Ⅲ组（P〈0．01）；Ⅲ组产后1d和28d显著高于Ⅰ组（P〈0．01或P〈0．05）。这些结果表明，围产期奶牛能量摄入水平对肝MTP mRNA丰度有显著影响。  相似文献   

8.
The effect of parity on the cervical and uterine involution was studied in 79 Finnish dairy cows on a research farm. The cows were examined clinically by rectal palpation 3 times a week during 8 weeks postpartum. The diameters of the cervix and uterine horns were estimated manually. The parous uterine horn was compared with the non-parous one. The results were separately analysed in primiparous cows (n = 18) and in those with the third calving (n = 61). A significant difference (p less than 0.001) between the parous and non-parous uterine horns was obtained until 21 days. Thereafter, involution still continued and equal diameters for the horns were not found until 5 weeks after parturition. A decline of the cervical diameter continued until 30 days after the delivery. The parity had no significant effect on the swiftness of uterine or cervical involution. However, in multiparous cows the cervical diameter remained larger than that in the primiparous animals still at 8 weeks postpartum.  相似文献   

9.
Thirteen primiparous and 41 multiparous Holstein-Friesian cattle were used to study the relationship between maternal plasma progesterone (P4) and estrone sulfate (E1S) concentrations and the prevalence of dystocia. The calvings in 4 heifers and 30 cows were normal (eutocia), while the calvings in 9 heifers and 11 cows were difficult (dystocia). Neither the concentrations of P4 nor E1S were different between the groups with eutocia and dystocia from days 90 to 270 of pregnancy. However, a few days prior to parturition, eutocial cows and heifers showed a sharp decline of plasma P4, while dystocial cattle did not show such a remarkable decline of P4 concentration. Plasma P4 levels in dystocial cows a few days antepartum were significantly higher than in eutocial animals (P<0.05 or P<0.01). Prepartum E1S concentrations were significantly lower (P<0.05) in dystocial than eutocial cattle during the prepartum period from days 6 to 1 in heifers and from days 3 to 1 in cows. These results suggest that insufficient production of E1S and delayed regression of the corpora lutea are possible causes of dystocia in cattle.  相似文献   

10.
The objective of this experiment was to study the effect of prepartum diets on dry matter intake (DMI) around parturition and on milk production in early lactation during a hot summer. Nine cows due to calve in July or August were assigned to two groups and fed either control (group C; four cows) or high‐concentrate (group H; five cows) diets to meet 110% of their energy requirements from 18 days before the expected calving date to parturition. The proportion of concentrate in the control diet was 35%, and that in the high‐concentrate diet was 45%. For 21 days after parturition, all cows were fed the same diets for lactation ad libitum. The DMI of cows in group H almost met their energy requirements. In group C, the DMI was decreased relative to group H and the concentration of plasma non‐esterified fatty acids was significantly higher (P < 0.05) before parturition. Therefore, the cows in group C were thought to be energy deficient before parturition. After parturition, there were no significant differences in DMI between the two groups. The milk yield of cows in group H tended to be higher than that of cows in group C at 21 days after parturition. Milk protein yield was significantly higher (P < 0.05) in group H 21 days after parturition relative to group C. There were no significant differences in milk composition between the two groups.  相似文献   

11.
将年龄、胎次相同,年产奶量大于5000kg的围产期健康奶牛30头随机分为3组,每组10头。按照中国奶牛饲养标准(2000),低能组饲喂减少20%日粮(能量摄入80%组),对照组饲喂标准日粮(能量摄入100%组),高能组饲喂增加20%日粮(能量摄入120%组),试验从产前14天开始至产后28天结束,产后各组奶牛均饲喂标准日粮。采用半定量RTPCR方法检测了不同能量摄入对围产期奶牛脂肪组织胰岛素受体(InsR)mRNA丰度的影响。结果表明:各组脂肪InsRmRNA相对表达量从产前14天至产后28天均呈现先升高后降低的趋势,产后14天达到最大值,且产后高于产前;低能组产前InsRmRNA相对表达量低于高能组和正常组,产后1天至产后28天高于高能组和正常组,产后14天显著高于高能组(P<0.01)。可见,干乳期低能饲喂奶牛,产后脂肪InsRmRNA表达增加,提示产前适当降低能量摄入水平,有利于胰岛素抑制泌乳初期脂肪动员作用的发挥。  相似文献   

12.
This study determined colostrum production of lactating primiparous and multiparous Holstein dairy cows, as well as the predictability of full lactation milk yield based upon this colostrum production. Holstein cows that calved between December 18, 2006 and December 24, 2007 (n = 134) had their first two post-partum milkings weighed and assayed for density. Cows then entered normal production groups and were assessed for milk yield and milk components every 4 or 5 weeks for the duration of their lactation. Primiparous cows produced less colostrum (10.6 versus 13.6 kg; P = 0.02) and density adjusted (DA) colostrum (5.2 versus 8.5 kg; P < 0.01), but there were no differences in estimated 305 day mature equivalent (305ME) milk production (mean = 13,654 kg) or lactation lengths (mean = 301 days) between parities. Colostrum and DA colostrum were poor estimators of subsequent 305ME milk production within primiparous cows (r2 = 0.20 and 0.01 respectively) and multiparous cows (r2 = 0.18 and 0.12 respectively). Colostrum production of these high producing cows was somewhat lower than expected, highly variable among cows within parity, higher for multiparous versus primiparous cows, and was not a good estimator of subsequent 305ME milk production.  相似文献   

13.
Metabolic hormones affect ovarian function in the cow. However, the relationship between metabolic factors and ovarian function is not clear in the postpartum primiparous cow because they are still growing. The aim of the present study was to investigate in detail the time-dependent profile of the metabolic hormones, metabolites, and milk yields of ovulatory and anovulatory primiparous cows during the first follicular wave postpartum. We used 16 primiparous Holstein cows and obtained blood samples for the profiles of metabolites (glucose; non-esterified fatty acid, NEFA; ketone body; total cholesterol; and aspartate aminotransferase), metabolic hormones (growth hormone, GH; insulin-like growth factor-I, IGF-1; and insulin), and progesterone every other day from 1 to 21 days postpartum. In addition, all ovaries were observed using ultrasound. Dairy milk yield was recorded during the experimental period. In all cows, the first follicular wave postpartum was observed and 6 of the cows ovulated. The plasma glucose (P<0.0001) and IGF-1 (P<0.001) concentrations were lower and the plasma NEFA (P<0.0001) and ketone bodies (P<0.0001) concentrations and daily milk yield (P<0.0001) were higher in the anovulatory cows compared to the ovulatory cows. However, the GH levels, which enhance lipolysis for milk production, insulin and other metabolites did not differ between the two groups. In conclusion, the present study suggests that anovulation of the dominant follicle during the first follicular wave postpartum in primiparous cows is induced by low IGF-1 levels that are similar to those of multiparous cows. In addition, anovulatory cows are likely to mobilize body fat stores for milk production more easily than ovulatory cows.  相似文献   

14.
The objective was to evaluate the effect of body condition score (BCS) at 30 days before calving (−30 days) induced by a differential nutritional management, parity and week of lactation (WOL) on milk yield and composition, and milk casein and fatty acid composition. Primiparous and multiparous Holstein cows with high BCS (PH, n = 13; MH, n = 9) and low BCS (PL, n = 9; ML = 8) under grazing conditions were sampled at WOL 2 and 8 (before and after peak of lactation). Milk yield was greater in multiparous than in primiparous cows and tended to decrease from WOL 2 to 8 only in ML cows. Milk protein, fat and casein yields were greater in multiparous than in primiparous cows and decreased from WOL 2 to 8. Milk casein concentration in milk protein was greater in MH cows than in ML, PH and PL cows at WOL 2. Milk κ‐casein was greater, and β‐casein was less in multiparous than in primiparous cows. As lactation progressed, proportion of casein fractions were not altered. Only κ‐casein fraction was affected by BCS at −30 days as PL showed a higher concentration than PH. The de novo (4:0–15:1) and mixed‐origin fatty acids (16:0–16:1) in milk fat increased, whereas preformed fatty acids (≥17:0) decreased from WOL 2 to 8. Saturated (SAT) fatty acids tended to be greater and monounsaturated fatty acids (MUFA) were less in multiparous than in primiparous cows. High‐BCS cows had greater concentrations of polyunsaturated (PUFA), conjugated linoleic acid (CLA) as well as n‐6 and n‐3 fatty acids in milk fat than low‐BCS cows. The results indicate that casein and fatty acid fractions in milk were affected by parity and may be modified by a differential nutritional management during the pre‐calving period (BCS at −30 days) in cows under grazing conditions.  相似文献   

15.
The acyclic postpartum period in cows is prolonged due to frequent suckling when compared with twice daily milking. In conventional milking systems twice daily milking is common, while in automatic milking systems (AMS) three or more milkings are performed in early lactation. In this study, the hypothesis was tested that an increased milking frequency in AMS causes a delay in resumption of ovarian cyclicity postpartum and increases days open in German Fleckvieh cows (n = 124). Calvings were equally distributed throughout the 1-year experimental period. All cows were housed in one barn. Sixty-three cows were milked in an AMS (AC) and 61 cows were twice daily milked in a conventional milking parlour (PC). Forty-two AC and 36 PC remained in the herd until conception. After parturition, milk samples were analysed for progesterone twice weekly to record the ovarian activity until pregnancy was diagnosed. The first and the second ovulation were determined by the progesterone profile of each individual cow. The mean milking frequency during the first 3 weeks after parturition was higher in AC (3.17 +/- 0.09 milkings/day) than in PC (milked twice daily). The individual mean milking frequency of AC for the first 3 weeks of lactation ranged from 2.0 to 5.9 daily milkings. The time span from parturition until the first and second ovulation did not differ between AC and PC. However, first ovulation was observed earlier in primiparous (23 +/- 1 days) than in multiparous cows (29 +/- 1 days, P < 0.05). Within AC no relationship between milking frequency and duration of the acyclic period was observed. Days open did not significantly differ between AC and PC and between primiparous and multiparous cows. In conclusion, the increased milking frequency in AMS did neither cause a delay in resumption of ovarian cyclicity postpartum nor did it increase days open.  相似文献   

16.
We investigated the effect of heat stress on Ca, P and Mg balance and bone turnover in lactating cows. In a 2 × 2 crossover design, four multiparous lactating Holstein cows were kept in a chamber and subjected to a constant moderate (18°C) ambient temperature (MT) or high (28°C) ambient temperature (HT). The cows were fed total mixed ration (Ca, 0.7%; P, 0.4%; Mg, 0.2%) ad libitum. The milk yield under HT (35.4 kg/day) tended to be lower (P < 0.10) than that under MT (43.2 kg/day). The concentrations of milk P (P < 0.05) and Mg (P < 0.01) were significantly lower under HT than MT. The Ca, P and Mg intake (P < 0.10); Ca (P < 0.10), P, and Mg (P < 0.05) secretion into milk; and Ca (P < 0.05), P (P < 0.01), and Mg (P < 0.05) absorption in the intestine were lower under HT than MT. The plasma osteocalcin, a marker of bone turnover, was significantly lower (P < 0.05) under HT than MT. Heat stress did not affect plasma C‐telopeptide of collagen type I, a bone resorption marker, and plasma parathyroid hormone concentration.  相似文献   

17.
Intake of polyunsaturated fatty acids (PUFA) could modify follicular dynamics and reduce the length of the interval from calving to first ovulation (ICOV) in dairy cows, associated with changes in metabolites (i.e. cholesterol) or hormones (i.e. IGF-I). To test this hypothesis, 48 cows were stratified in two groups (primiparous or multiparous) and within each group were randomly assigned to three treatments to begin at calving: 0 kg (SS0), 0.7 kg (SS0.7) and 1.4 kg (SS1.4) of whole sunflower seeds (WSS) per cow per day. The experimental period lasted for 60 days after calving and the diets, which consisted of direct grazing of improved pastures, whole-plant wheat silage and concentrates, were designed to be isocaloric and isoproteic (1.6 Mcal NEL/kg DM, 16.7% CP). Ovaries were examined by ultrasound three times per week from day 8 postpartum (PP) until first PP ovulation. Body condition score (BCS) was determined and blood samples were collected weekly from calving to characterize the metabolic profiles. In treatments SS0.7 and SS1.4, 7/8 and 6/8 primiparous cows ovulated the first follicular wave PP, compared with only 1/8 primiparous cow in treatment SS0, while there were no treatment differences in multiparous cows. The ICOV was 44, 21 and 19 days for the primiparous, and 22, 21 and 25 days for the multiparous cows, in treatments SS0, SS0.7 and SS1.4, respectively. Treatments had no effect on BCS, plasma IGF-I and metabolic profiles except that NEFA and urea were increased by WSS supplementation. Intake of PUFA (WSS up to 1.4 kg/day or 6.7% of the diet) during early lactation reduced the ICOV in primiparous grazing dairy cows in early lactation but not in multiparous cows, and while the precise mechanism for these results is unclear, it was not related to changes in the plasma concentrations of IGF-I or cholesterol.  相似文献   

18.
本研究旨在探明和田多胎红羊泌乳规律,提高双羔成活率。选取6只产双羔和田多胎红羊母羊为试验动物,检测其产后1~28 d泌乳量、乳成分变化规律;测量产后第1天母羊乳房体尺指标,并与泌乳量进行相关性分析。结果显示,和田多胎红羊产后1~28 d总泌乳量为29.87 kg,平均每日泌乳量为1.07 kg,泌乳量在第1~3天上升速度最快,在第21天达到峰值1.23 kg,泌乳曲线方程为：y=537t0.477e-0.033t;乳脂、非脂乳固体、密度、乳糖、固形物、蛋白质指标在和田多胎红羊母羊产后1~3 d快速下降,7~28 d趋于稳定,且6项指标第1天与第7、14、21、28天均差异极显著（P<0.01）;和田多胎红羊母羊产后第1天与第14、21、28天的泌乳量之间相关性不显著（P>0.05）,产后第2天与第28天的泌乳量相关性不显著（P>0.05）,其他均显著相关（P<0.05）;母羊产后第1、2、3、7天泌乳量与乳房宽呈显著相关（P<0.05）,母羊产后第14、21、28天泌乳量与乳房体尺指标相关性不显著（P>0.05）。以上研究结果为和田多胎红羊新类群种质特性、选育、饲料配制、羔羊早期断奶等提供理论依据。  相似文献   

19.
We evaluated age-related changes in serum osteocalcin concentrations in non-periparturient cows and variations in serum osteocalcin concentration in periparturient primiparous and multiparous cows. The serum osteocalcin levels were evaluated in 144 non-periparturient Holstein dairy cows aged 11 days to 10 years; these levels were the highest in the youngest cows, appeared to steadily decrease with age until the time of the first calving, and were subsequently maintained at low levels. Between 14 days before calving and 21 days after calving, the serum osteocalcin levels were significantly higher in the primiparous cows than in the multiparous cows. A comparison between age-matched non-periparturient and periparturient cows showed that serum osteocalcin levels were significantly lowered during late gestation in both primiparous and multiparous cows. These results suggest that serum osteocalcin measurement might be useful for the detection of mineral imbalances at the time of parturition in cows.  相似文献   

20.
Brangus cows (n = 29) were used in three experiments to evaluate the effects of parity (multiparous vs. primiparous) and potential genetic merit for milk production (high vs. low) on forage intake during late gestation, early lactation, and late lactation. Cows were selected for milk production based on their sire's EPD for milk production (MEPD). Cows had ad libitum access to (130% of previous 2-d average intake) low-quality hay (5.3% CP and 76% NDF), and cottonseed meal was supplemented to ensure adequate degradable intake protein. All females were adapted to diets for at least 7 d, and individual intake data were collected for 9 d. During the lactation trials, actual milk production was determined using a portable milking machine following a 12-h separation from calves. During late gestation, multiparous cows consumed 24% more (P = 0.01) forage DM (kg/d) than primiparous cows; however, parity class did not influence forage intake when intake was expressed relative to BW. Furthermore, MEPD did not influence forage intake during late gestation. During early lactation, multiparous cows produced 66% more (P < 0.001) milk than primiparous cows, and high MEPD tended (P = 0.10) to produce more milk than low MEPD. Multiparous cows consumed 19% more (P < 0.0001) forage DM than did primiparous cows when expressed on an absolute basis, but not when expressed on a BW basis. High-MEPD cows consumed 8% more (P < 0.05) forage DM than did low-MEPD cows. During late lactation, multiparous cows produced 84% more milk than primiparous cows, although MEPD did not influence (P = 0.40) milk yield. In addition, multiparous cows consumed 17% more (P < 0.01) forage DM per day than primiparous cows, but when intake was expressed relative to BW, neither parity nor MEPD influenced forage DMI during late lactation. Milk yield and BW explained significant proportions of the variation in forage DMI during early and late lactation. Each kilogram increase in milk yield was associated with a 0.33- and 0.37-kg increase in forage DMI for early and late lactation, respectively. Results suggest that multiand primiparous cows consume similar amounts of low-quality forage DM, expressed per unit of BW, during late gestation and lactation. Selecting beef cows for increased genetic merit for milk production increases forage DMI during early lactation.  相似文献   

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