Evaluation of age, weaning weight, body condition score, and reproductive tract score in pre-selected beef heifers relative to reproductive potential

Background: Artificial insemination is a preferred breeding method for beef heifers as it advances the genetic background, produces a predictive and profitable calving season, and extends the heifer’s reproductive life span.As reproductive efficiency in heifers is key for the success of beef cattle production systems, following artificial insemination, heifers are exposed to a bull for the remainder of the breeding season. Altogether, up to 95% of heifers might become pregnant in their first breeding season. Heifers that do not become pregnant at the end of the breeding season represent an irreparable economical loss. Additionally, heifers conceiving late in the breeding season to natural service, although acceptable, poses serious losses to producers. To minimize losses due to reproductive failure, different phenotypic parameters can be assessed and utilized as selection tools. Here, we tested the hypothesis that in a group of pre-selected heifers, records of weaning weight, age at weaning, age at artificial insemination, and age of dam differ among heifers of varied reproductive outcomes during the first breeding season.Results: None of the parameters tested presented predictive ability to discriminate the heifers based on the response variable(‘pregnant to artificial insemination’, ‘pregnant to natural service’, ‘not pregnant’). Heifers categorized with body condition score = 6 and reproductive tract score ≥ 4 had the greatest proportion of pregnancy to artificial insemination(49% and 44%, respectively). Furthermore, it was notable that heifers presenting body condition score = 6 and reproductive tract score = 5 presented the greatest pregnancy rate at end of the breeding season(89%). Heifers younger than 368 d at the start of the breeding season did not become pregnant to artificial insemination. Those young heifers had 12.5% chance to become pregnant in their first breeding season,compared to 87.5% if the heifers were older than 368 days.Conclusion: Our results suggest that beef heifers with body condition score = 6 and reproductive tract score ≥ 4 are more likely to become pregnant to artificial insemination. Careful assessment should be undertaken when developing replacement heifers that will not reach 12 months of age by the beginning of the breeding season.

N-carbamylglutamate restores nitric oxide synthesis and attenuates high altitudeinduced pulmonary hypertension in Holstein heifers ascended to high altitude

Background: High-altitude pulmonary hypertension(HAPH) is a life-threating condition for animals in high altitude,and disturbance of endothelial nitric oxide(NO) synthesis contributes to its pathogenesis. N-carbamylglutamate(NCG), which enhances arginine synthesis, promotes endogenous synthesis of NO. In this study, we determined the effects of NCG on alleviating HAPH in Holstein heifers that ascended to Tibet(Lhasa, 3,658 m).Methods: Exp. 1, 2,000 Holstein heifers were transported from low elevation(1,027 m) to Lhasa. After being exposed to hypoxia for 1 yr, Holstein heifers were assigned to a healthy group(Control, n = 6) with mean pulmonary hypertension(mPAP) < 41 mmHg, and an HAPH affected group(HAPH, n = 6) with mPAP > 49 mmHg.Lung tissues were collected to evaluate histopathological changes and the expression of endothelial nitric oxide synthase(eNOS). Exp. 2, ten healthy heifers and 10 HAPH affected heifers were supplemented with NCG(20 g/d per heifer) for 4 wk. Physiological parameters were determined and blood samples were collected on d-1 and d 28 of the feeding trial.Results: Expression of e NOS in small pulmonary arteriole intima was higher in the healthy than HAPH group(P = 0.006), whereas HAPH group had significantly thicker media and adventitia than healthy group(all P < 0.05). The mRNA of eNOS and protein level of eNOS were higher in the lungs of heifers in the healthy group than in the HAPH group(both P < 0.001), whereas endothelin-1 protein levels were higher in HAPH group than in the healthy group(P = 0.025). NCG supplementation decreased mPAP and ammonia(both P = 0.001), whereas it increased the expression of eNOS, arginine, and plasma NO(all P < 0.05).Conclusions: The expression of eNOS was decreased in Holstein heifers with HAPH. NCG supplementation decreased m PAP through the restoration of eNOS and endogenous NO synthesis.

Association of a missense mutation in the luteinizing hormone/choriogonadotropin receptor gene (LHCGR) with superovulation traits in Chinese Holstein heifers

Background： Upon binding luteinizing hormone in the ovary, the luteinizing hormone/choriogonadotropin receptor （LHCGR） is necessary for follicular maturation and ovulation, as well as luteal function. We detected mutations in the LHCGR gene and evaluated their association with superovulation. Methods： Using polymerase chain reaction-single strand sequencing, we examined polymorphisms in LHCGR and Chinese Holstein heifers. conformation polymorphism （PCR-SSCP） and DNA the genotypes associated with superovulation traits in 127 Results： A G/T polymorphism （ss52050737） in exon 11 was significantly associated with the total number of ova and the number of transferable embryos. Conclusions： LHCGR may be a new predictor for superovulation in Chinese Holstein heifers.

A Study of Dairy Heifer Rearing Practices from Birth to Weaning and Their Associated Costs on UK Dairy Farms

There are many inputs into the dairy replacement herd which impact not only on the cost of rearing heifers from birth to first calving, but also on their future longevity and production potential. This study determined the current cost of rearing dairy heifers in the UK through the calculation and analysis of individual costs on a subset of 102 UK dairy farms. Each farm was visited and an extensive heifer rearing questionnaire was completed. Current heifer rearing practices were recorded to provide insight into critical management decisions. A cost analysis workbook was developed to calculate the costs of inputs in the preweaning period for labour, calving, feed, housing, health treatments and vaccinations, waste storage, machinery and equipment, and utilities. The average age at weaning was 62 d. The mean cost of rearing from birth to weaning was ￡195.19 per heifer with a mean daily cost of ￡3.14 (excluding the opportunity cost of the calf). This ranged from ￡1.68 to ￡6.11 among farms, reflecting major differences in management strategies and efficiency. The highest contribution to total costs came from feed (colostrum, milk, starter and forage) at 48.5% with milk feeding making up the greatest proportion of this at 37.3%. The next major expenses were bedding and labour, contributing 12.3% and 11.2% respectively. Unsurprisingly, delaying age at weaning increased total cost by ￡3.53 per day. Total costs were on average 45% higher on organic farms than conventional due to higher feed costs and later weaning. Calving pattern also had a strong association with the total cost being lowest with spring calving, intermediate with autumn calving and highest in multi block and all year round calving herds.

Heat stress on calves and heifers: a review

The current review is designed with aims to highlight the impact of heat stress(HS) on calves and heifers and to suggest methods for HS alleviation. HS occurs in animals when heat gain from environment and metabolism surpasses heat loss by radiation, convection, evaporation and conduction. Although calves and heifers are comparatively heat resistant due to less production of metabolic heat and more heat dissipation efficiency, they still suffer from HS to some degree. Dry matter intake and growth performance of calves and heifers are reduced during HS because of redistributing energy to heat regulation through a series of physiological and metabolic responses, such as elevated blood insulin and protein catabolism. Enhanced respiration rate and panting during HS accelerate the loss of CO2, resulting in altered blood acid-base chemistry and respiratory alkalosis. HS-induced alteration in rumen motility and microbiota affects the feed digestibility and rumen fermentation. Decreased luteinizing hormone, estradiol and gonadotrophins due to HS disturb the normal estrus cyclicity, depress follicular development, hence the drop in conception rate. Prenatal HS not only suppresses the embryonic development by the impaired placenta, which results in hypoxia and malnutrition, but also retards the growth, immunity and future milk production of newborn calves. Based on the above challenges, we attempted to describe the possible impacts of HS on growth, health, digestibility and reproduction of calves and heifers. Likewise, we also proposed three primary strategies for ameliorating HS consequences. Genetic development and reproductive measures, such as gene selection and embryo transfers, are more likely long-term approaches to enhance heat tolerance. While physical modification of the environment, such as shades and sprinkle systems, is the most common and easily implemented measure to alleviate HS. Additionally, nutritional management is another key approach which could help calves and heifers maintain homeostasis and prevent nutrient deficiencies because of HS.

Association between growth rates, age at first calving and subsequent fertility, milk production and survival in Holstein-Friesian heifers

Age at first calving (AFC) affects the profitability of dairy enterprises. This study examined the relationships between AFC and subsequent fertility, milk production and survival up to third calving in UK Holstein-Friesian heifers;Study 1 comprised 134 consecutively born heifers from the same herd (AFC 764 ± 8 days) and Study 2 contained 445 heifers born on 17 farms (AFC 796 ± 6 days). Growth rates and fertility during rearing were monitored and animals were subsequently divided into four AFC groups for analysis: <23 months, 23 - 25 months, 26 - 30 months and >30 months. The actual AFC reflected both growth rate and heifer fertility, with later calving heifers already lighter by 6 months of age. The proportion conceiving to first service was highest (93% and 84% for Studies 1 and 2, respectively) for the youngest AFC group. Fertility in the first lactation was best in cows calving at 23 - 25 months and worst in the oldest AFC group. Milk production parameters in the first and second lactations were broadly similar between AFC groups but significantly more heifers with an AFC < 26 months calved for a third time. These younger calving animals therefore achieved more days in milk over 5 years, with >44% of their days alive spent in milk production compared with only 18% - 40% in cows calving at ≥26 months. Hence cows with an AFC < 26 months produced the most milk in their first 5 years of life. These results indicate that an AFC of 0.75 kg/d up to 15 months and good heifer fertility and resulted in the best subsequent performance.

The Management and Associated Costs of Rearing Heifers on UK Dairy Farms from Weaning to Conception

Dairy heifers only start to produce a return on investment at first calving. The length of the non-productive rearing period is largely governed by farmer decisions on plane of nutrition and reproduction management. Primary data were collected from 101 dairy farms and a cost analysis workbook developed to calculate individual inputs in each of three periods to determine which management decisions and farm factors have the greatest influence on the total costs associated with rearing. This paper covers weaning until conception. Heifers were weaned at 62 d (range 42 - 112 d) and conceived by 509 d (range 365 - 700 d) giving an average weaning to conception period of 447 ± 60 d (range 253 to 630 d). The mean daily cost of rearing during this period was ￡1.65 (range ￡0.75 to ￡2.97 on different farms) giving a mean total cost of ￡745.94 per heifer (range ￡295.32 to ￡1745.85). This large variation was mostly due to the duration, which was mainly determined by age at first breeding (mean 476 days, range 365 - 700 d). The main contributors to total costs were feed (35.6%), labour (24.7%) and bedding (8.9%). The variables most strongly associated with the total costs were age at conception, calving pattern and breed. A multivariable model predicted an increase in mean cost of ￡2.26 for each extra day in age at conception. The total cost was highest in herds with all year round calving, intermediate in multi-block and lowest in spring and autumn calving herds, with Friesian x and Jersey herds having the lowest cost of rearing.

Effect of mammary stimulation on dairy cows and heifers exposed to a lactation induction protocol

Cows (n = 21), dried off for a minimum of 45 days, and nulliparous heifers (n = 26), at ages > 18 months old, were placed on a 12-day Lactation Induction (LI) protocol. One group of animals (including both cows and heifers) received 3-minute mammary gland stimulation, along with the LI protocol. Another group, again including both cows and heifers, received no stimulation only the LI protocol This consisted of two injections of prostaglandin F2α (PGF2α;25 mg) 11 days apart, followed by subcutaneous injections of 17β-estradiol (0.1 mg/kg BW/d) and progesterone (0.25 mg/kg BW/d) beginning 1 day later and continuing for seven (7) days. After this step, all animals received another injection of PGF2α on day 8, followed by intramuscular injections of reserpine (5 mg/d) and dexamethasone (20 mg/d) on each of days 9 to 12. All animals were milked, beginning on day 13, for a period of 154 days. For all animals, the success rate for lactation induction was 78% ± 6.3% and the mean weekly milk yield was 78.2 kg. Neither value was affected by mammary stimulation. Parity did not significantly impact on the success rate but it did affect the mean weekly milk yield. Milk yield varied significantly (p < 0.001) with week, peaking during week 9. Peak milk production and persistency were 101.6 kg ± 5.9 kg and 16.9 weeks ± 2.4 weeks respectively, with neither being significantly (α = 0.05 level) affected by stimulation or by parity. However, heifers (at 8.2 weeks ± 1.0 week) tended (p = 0.1) to reach peak milk production earlier than cows (at 10.7 weeks ± 1.3). The milk produced was sold at a net profit per animal treated of $2206.31 TT. Hence, one can conclude that a Lactation Induction protocol can be a useful management tool to increase production and profitability of dairy operations in the tropics.

Analysis of the Management and Costs Associated with Rearing Pregnant Dairy Heifers in the UK from Conception to Calving

Good management of the pregnant heifer is crucial to ensure that she is well grown and healthy and calves down easily before joining the milking herd. This study collected primary data on all aspects of heifer management on 101 UK farms during heifer pregnancy from conception to calving including farm factors and associated costs of system inputs. A cost analysis workbook was developed to calculate the cost of rearing per heifer for each of the study farms. Associations between cost of rearing and farms factors were determined using linear regression and analysis of variance. Heifers had a mean age of conception of 509 d (range 365 - 700 d) and an age at first calving of 784 d (range 639 - 973 d). The mean total cost of rearing during pregnancy was ￡450.36 (range ￡153.11 to ￡784.00) with a mean daily cost of ￡1.64 (range ￡0.56 to ￡2.86). The inputs contributing the most to cost were feed (32.7%), labour (23.8%) and slurry disposal (11.2%). Total purchased and homegrown feed and grazing contributed between 25.5% and 65.4% of total costs with a mean contribution of 43.6%. The cost of rearing was lowest in spring calving herds and highest in all year round calving herds with intermediate values in autumn and multi block calving herds. The main variables influencing the cost were the number of days spent at grass, age at first calving, calving pattern, breed, herd size and region. Each extra day in age at first calving increased the mean cost of rearing during pregnancy by ￡0.33/d whereas every extra day at grass reduced the cost by ￡1.75/d.

Heifer Body Weight Gain and Reproductive Achievement in Response to Protein and Energy Supplementation While Grazing Dormant Range Forage

Heifers grazing winter range require supplemental nutrients to complement dormant forage to achieve optimal growth and performance. A study was conducted to evaluate nutritional environment and effect of different supplementation strategies for developing heifers grazing dormant winter range. Eighty-four Angus crossbred heifers were stratified by body weight at weaning, allocated to one of six replicated pastures, and randomly assigned one of three supplemental treatments: 1) 908 g/d of a control supplement providing 340 g·hd-1·d-1 of CP with 130 g of rumen undegradable protein (RUP) and 614 MJ of ME (LRUP);2) 908 g/d of a RUP supplement providing 340 g·hd-1·d-1 of CP with 170 g of RUP and 567 MJ of ME (HRUP);or 3) 1814 g/d of a protein and energy supplement providing 340 g·hd-1·d-1 of CP with 120 g of RUP + 100 g of propionate salt (NutroCalTM, Kemin Industries, Inc.) and 1222 MJ of ME (LRUP + E). Body weights were taken in November, with monthly 12 h shrunk BW from January thru April, and again in September (at time of pregnancy diagnosis). Heifer average daily gain was similar throughout the developmental period except from d125 to d159 where LRUP + E supplemented heifers had greater gains

Preference, Feeding Behavior, and in Vitro Fermentation Characteristics of Pelleted Feeds Containing Alkaline Aqueous Lignin By-Product from Paper Processing in Holstein Heifers

The objectives of this study were to evaluate the effect of using multiple dietary inclusion rates of alkaline aqueous lignin by-product(AALB),in replacing a commercial binder,on the preference and feeding behavior of dairy heifers,and in vitro digestibility.In the experiment I,five pelleted diets including negative control(no-binder),commercial lignosulfonate binder,and 1.6%,3.2%,and 4.8%of AALB were tested.In the experiment II,five pelleted diets including negative control,positive control(2%molasses),and 1%,2.4%,and 3.8%of AALB(all combined with 2%of molasses)were tested.Feeding behavior and preference were determined for 60 min per animal per evaluation.In vitro digestibility was determined for each pelleted diet for 48 h over five incubation runs.Results from Experiment I showed animals receiving 1.6%of AALB diet showed the greatest preference(dry matter(DM),intake)and a greater number of approaches with eating than other diets.The preference was lower when animals received control or 4.8%AALB diets relative to other diets.Results from Experiment II revealed animals receiving 3.8%AALB combined with molasses showed the greatest DM intake preference over 60 min,and DM intake per approach.Diets that included 2.4%and 3.8%of AALB combined with molasses presented the greatest in vitro DM digestibility.Overall,heifers showed a greater intake when receiving pelleted diets with 1.6%AALB.Furthermore,preference,intake over 60 min,and in vitro DM digestibility,were greater in the pelleted diets that contained higher rates of AALB when combined with molasses.

Assessment of Negative Training on the Use of Cubicle Beds by Heifers

40 in-calf heifers were observed to examine the effect of timbers placing in passage area on their use of cubicle beds. Prior to the experiment preliminary observation was taken on these 40 heifers and they were divided into two even groups (cubicle user(or control) group versus cubicle refusal (or experimental) group by whether they properly used the cubicle beds or not. The timbers were placed in passage and feeding areas for the cubicle refusal group to force the animls to lie in the cubicle beds. The results of this experiment showed that feeding behaviour was unaffected by the presence of the timbers, but lying acitvity was about 8% higher for the experimental group, which led to a mean of almost 2 hours longer lying time over 24 h. After the timbers were removed, there was a significant decline in lying by the experimental group. The diurnal pattern of lying behaviour in cubicles indicated that the major effect on lying activity exerted by the presence of the timbers was seen during midnight to 10:00 am. Also during this times, the experimental group in the pres-ence of the timbers tended to show more lying in cubicles than control group. At the end of the experiment, 95% of the heifers were found to be correctly using the cubicle beds, and on the negative side three heifers developed a slight injury on their legs or hocks caused by the timber.

Methane Emissions from Grazing Holstein-Friesian Heifers at Different Ages Estimated Using the Sulfur Hexafluoride Tracer Technique

动物和日粮因素对牛肠道甲烷排放量影响的相关研究已经很普遍,但是关于放牧青年奶牛的甲烷排放量的可参考数据较少。本研究评估了荷斯坦奶牛在多年生黑麦草草地放牧时的生理状态对甲烷排放量的影响,分别进行了以下两个试验:试验1从2011年5月开始,为期11个星期,试验2从2011年8月开始,为期10个星期。在每个试验中,将荷斯坦奶牛分成三个处理组(每组12头),分别由小牛犊、一岁的母牛犊和妊娠母牛组成(平均年龄分别为8.5、14.5和20.5月龄)。在每个试验的最后一个星期利用六氟化硫示踪技术预估每头牛的甲烷排放量。干物质摄入量由代谢能需要量除以牧草中的代谢能含量计算而得。正如预期一样,活体重随年龄的增加而增加(P<0.001),然而试验1中三个分组的体增重没有差异,试验2中的体增重随着年龄增加有不同程度的减少(P<0.001)。在试验1中,妊娠母牛高于小牛犊的甲烷排放量(P<0.001),而一岁母牛犊的甲烷排放量最高(g·d^(-1))。当用单位活体重、干物质摄入量和总能摄入量表示甲烷排放量时,一岁母牛犊比小牛犊和妊娠母牛的排放速率更高(P<0.001)。在试验2中,甲烷排放量(g·d^(-1))随着年龄增加呈线性上升(P<0.001),但是这种差异在一岁母牛犊和妊娠母牛中并不显著。妊娠母牛的甲烷/活体重的比值低于另外两组(P<0.001),小牛犊的总能摄入量中甲烷能量输出的比值低于一岁母牛犊和妊娠母牛(P<0.05)。根据所有数据建立甲烷排放量的预测方程。所有关系均为显著(P<0.001),R2值的分布范围为0.630~0.682。这些模型表明:每增加1 kg活体重,甲烷排放量增加0.252 g·d^(-1);每增加1 kg·d^(-1)干物质摄入量,甲烷排放量增加14.9 g·d^(-1);每增加1 MJ·d^(-1)总能摄入量,甲烷能量输出增加0.046 MJ·d^(-1)。当实际甲烷排放量不可测时,这些结果为我们提供了预估放牧母牛甲烷排放量的另一种方法。

The crucial role of lysine in the hepatic metabolism of growing Holstein dairy heifers as revealed by LC-MS-based untargeted metabolomics

The objective of this experiment was to evaluate the effect of supplementing rumen-protected Lys based on a Lys-deficient diet on liver metabolism in growing Holstein heifers.The experiment was conducted for 3 months with 36 Holstein heifers(initial body weight:200±9.0 kg;7-month-old).Heifers were randomly assigned to 2 diets based on corn,soybean meal,alfalfa hay,and wheat bran:control,Lysdeficient diet(LD;0.66%Lys in diet),and Lys-adequate diet(LA;1.00%Lys in diet).The results showed no difference in growth performance between the 2 groups(P>0.05).However,there was a clear trend of increasing feed conversion rate with Lys supplementation(0.05<P<0.01).The serum urea nitrogen concentration was significantly decreased,and the aspartate aminotransferase-to-alanine aminotransferase ratio was significantly decreased by Lys supplementation(P<0.05).Moreover,growing heifers fed a Lys-adequate diet had lower levels of urine nitrogen excretion and higher levels of the biological value of nitrogen(P<0.05).Metabolomic analysis revealed that 5 types of phosphatidylcholine and 3 types of ceramide were significantly increased and enriched in sphingolipid metabolism and glycero phospholipid metabolism(P<0.05).His,Leu,and Asp levels were significantly decreased in the liver following Lys supplementation(P<0.05).In conclusion,Lys supplementation may promote the synthesis of body tissue proteins,as evidenced by significantly decreased amino acids in the liver and urine N excretion,it also improves hepatic lipid metabolism by providing lipoprotein precursors.

性控精液对奶牛体内胚胎质量、发育和移植妊娠率的影响

[目的]研究性控精液对奶牛体内胚胎质量、胚胎发育和胚胎移植妊娠率的影响。[方法]将144头青年奶牛随机分为对照组(63头)和试验组(81头),使用促卵泡激素(FSH,260 mg/头)进行超排处理。对照组和试验组分别使用常规精液和性控精液输精,并对获得的体内性控胚胎进行移植,对胚胎生产、胚胎质量、胚胎发育和胚胎移植妊娠情况进行统计。[结果]试验组供体获得的平均可用胚胎数(5.67枚)显著(P<0.05)低于对照组(6.92枚);试验组供体获得的可用胚胎中A级胚胎比例(62.53%)、B级胚胎比例(35.29%)与对照组(A级胚胎比例66.51%、B级胚胎比例30.97%)相比差异均不显著(P>0.05);试验组供体获得的可用胚胎中桑葚胚比例(84.10%)显著(P<0.05)高于对照组(61.24%),囊胚比例(15.90%)显著(P<0.05)低于对照组(38.76%);试验组的鲜胚移植妊娠率(52.41%)显著(P<0.05)低于对照组(66.13%)。[结论]与常规精液相比,使用性控精液生产奶牛体内性控胚胎并移植后,平均可用胚胎数、可用胚胎中囊胚比例和胚胎移植妊娠率降低,可用胚胎质量未明显降低;优化性控精液使用方案和胚胎移植技术能够提高体内性控胚胎生产和胚胎移植效率。

荷斯坦育成母牛结核性脑膜脑炎的病理学观察和病原鉴定

为了探究1例荷斯坦育成母牛结核性脑膜脑炎病例的病理变化并鉴定病原,本试验对1头24月龄病死荷斯坦育成母牛进行临床症状观察、尸体剖检和组织病理学观察,随后进行细菌分离培养,并通过抗酸染色和多位点PCR方法进行菌种鉴定。结果显示:发病牛临床表现共济失调、转圈、四肢及全身肌肉抽搐、眼球球结膜外突和角弓反张,病程数月;尸检可见脑底部表面、脑室内表面、肺脏、肾脏及后纵膈淋巴结表面和切面散在或密布大小不等的粟粒状黄白色结节;组织病理学观察结果显示,大脑、小脑、脑干、侧脑室和第四脑室的蛛网膜下腔内和局部脑实质内,以及肺脏、肾脏和后纵膈淋巴结内均有大小不等的典型结核性肉芽肿;将分离和纯培养的结核杆菌菌落制备涂片进行抗酸染色,可观察到散在或成簇红染的细长的分枝状小杆菌;分离菌株经结核分枝杆菌复合群(MtbC)的特异性多位点PCR鉴定为牛分枝杆菌。本试验在国内首次描述了由牛分枝杆菌引起荷斯坦育成母牛结核性脑膜脑炎病例的病理变化,为牛结核病的诊断和研究提供参考。

初次配种妊娠月龄对荷斯坦奶牛产奶量、繁殖性能和产后健康的影响

实验旨在研究初次配种妊娠月龄(AFP)对荷斯坦奶牛产奶量、繁殖性能和产后健康的影响。实验以内蒙古圣牧高科牧业有限公司2个规模化牧场1 876头荷斯坦青年母牛(A牧场1 004头,B牧场872头)为对象,将AFP分为5个组,分别为Ⅰ组(AFP<13.5)、Ⅱ组(AFP为13.5~14.0)、Ⅲ组(AFP为14.1~14.5)、Ⅳ组(AFP为14.6~16.0)、Ⅴ组(AFP>16.0),对比分析各组奶牛的平均产奶量、犊牛初生重、产后首次配种受胎率及产后疾病发生的数据。结果表明:2个规模化奶牛场以AFP≤16月龄为主(总占比为88.22%);AFP为13.5~14.0月龄时头胎牛的平均产奶量最佳,产后首次配种受胎率最高;AFP>16月龄时犊牛初生重最大,产后首次配种受胎率最低,产后胎衣不下的发生率最高;AFP<13.5月龄的奶牛产后真胃变位的发生率最高。综合以上结果,13.5~14.0月龄可能是荷斯坦青年牛适宜的初次配种月龄,这为规模化牧场选择合适的初次配种月龄提供了数据支撑。

不同生理阶段荷斯坦后备奶牛生长性能、营养物质表观消化率及瘤胃甲烷排放规律研究

本试验旨在研究不同生理阶段(18、21、24月龄)荷斯坦后备奶牛生长性能、营养物质表观消化率及瘤胃甲烷(CH4)排放规律。选用30头体况良好的荷斯坦后备奶牛,按照月龄和体重分为3个组(每组10头):18月龄组,体重为(512.2±11.9) kg;21月龄组,体重为(548.0±6.6) kg;24月龄组,体重为(608.1±6.0) kg。每个阶段的试验期为28 d,其中预试期7 d,正试期21 d。在每个试验期的第1、14、28天测定每头奶牛的体重,第26、27、28天连续采集饲粮和粪便样品,进行常规营养成分分析和营养物质表观消化率计算;采用GreenFeed测定系统测定每头奶牛瘤胃CH4和二氧化碳(CO_(2))排放量。结果表明:1)18、21、24月龄荷斯坦后备奶牛的体重、干物质采食量和总能摄入量随着月龄的增大而显著升高(P<0.05),平均日增重随着月龄的增大而显著降低(P<0.05)。2)18、21、24月龄荷斯坦后备奶牛干物质表观消化率随着月龄的增大而显著升高(P<0.05)。3)18、21、24月龄荷斯坦后备奶牛瘤胃CH4排放量、CH4/代谢体重、甲烷能和甲烷能/总能摄入量随着月龄的增大而显著升高(P<0.05)。综上所述,随着荷斯坦后备奶牛生理阶段的递进(18、21、24月龄),其瘤胃CH4排放量显著增加,主要原因可能是体重和干物质采食量的增加促进了CH4的合成。