Trends in the reproductive performance of Holstein dairy cows in Iran

The study was undertaken to determine the trends in the reproductive performance of Holstein dairy cows in Iran during 1994 to 2008. Reproductive performance data for 528,034 lactations of 246,132 cows in 1,822 Holstein dairy herds of Iran were used. The potential effect of calving season, herd, parity, calving year, as well as herd size and 305-day milk production on reproductive performance traits was investigated using multiple regression models. The least squares means of age at first calving decreased by 3.1 (±0.06) days per year from 806.5 (±96.3) days in 1994 to 788 (±89.9) days in 2008. The least squares means of calving interval increased 1.02 (±0.03) days per year from 394.1 (±65) days in 1994 to 413.2 (±81) days in 2008. Greater 305-day milk production was associated with an average increase of 6.55 (±0.08) days in calving interval per 1,000-kg increase in milk yield. Larger herd size was associated with an average decrease of 0.22 (±0.02) days in calving interval per 50 cows per herd. The mean number of days dry was 88.6 (±51.3) days and increased by 0.82 (±0.02) days per year. In conclusion, reproductive performance in Holstein dairy herds has generally decreased, whereas herd size and milk production have increased over time. Producers may make significant improvements in herd reproduction by reviewing management strategies including the sire selection, reproductive management, inseminator training and techniques, and improved estrous detection. Moreover, it may be advisable for the fertility traits to be included in the genetic selection indices to reduce the rate of reproductive decline.     

Incidence of subclinical endometritis and its effects on reproductive performance of crossbred dairy cows

In dairy cattle, uterine infections are not life threatening and often unavoidable; however, they reduce fertility and increase the production costs of properties. The aim of this study was to evaluate the incidence of subclinical endometritis from 32 to 70 days in milk (DIM) and its effects on the reproductive performance of crossbred dairy cows. Lactating cows (Holstein/Gir; n?=?172), with no history of retained placenta, without clinical signs of uterine infection were used. The body condition score (BCS) was evaluated on a scale from 1 to 5. Ultrasound examination was performed to evaluate uterine lining and ovarian activity, while vaginal mucus was analyzed by gloved hand. The diagnosis of subclinical endometritis was performed by endometrial cytobrush technique. The samples were collected, stained, and examined microscopically; positive cases for subclinical endometritis were considered with the presence of ≥5 % of neutrophils. Later, the cows were submitted to conventional artificial insemination or timed artificial insemination. The incidence of subclinical endometritis in the herd was 26 %, and this was not affected by the season of calving, presence of corpus luteum, DIM, and parity. Cows with a BCS ≤2.50 had a higher incidence of subclinical endometritis. The conception rate to first insemination and pregnancy rate at 150 days postpartum were not influenced by the presence of subclinical endometritis in crossbred dairy cows.     

Subclinical endometritis in Zebu x Friesian crossbred dairy cows: its risk factors,association with subclinical mastitis and effect on reproductive performance

A study was carried out on 59 clinically healthy Zebu x Friesian crossbred cows to determine the prevalence of subclinical endometritis, associated factors and its effect on the reproductive performance. Subclinical endometritis was diagnosed by endometrial cytology using uterine lavege technique and subclinical mastitis using CMT. The clinical, management and reproductive data were obtained from a weekly follow up visit of each cow for a period of 6 months after calving. The prevalence of subclinical endometritis, with ≥5% neutrophil count, was 47.5% and 30.5% at week 4 and 8, significantly decreasing (P = 0.002) as postpartum period advanced. Body condition score at week 4 postpartum (OR = 4.5, P = 0.017) and regular cow exercise (OR = 4.8, P = 0.026) were the significant risk factors while post-calving hygiene (P = 0.06) was poorly associated. Subclinical endometritis was also directly associated with subclinical mastitis at both week 4 (OR = 4.5, P = 0.012) and 8 (OR = 3.6, P = 0.031) postpartum. The risk of first service pregnancy (OR = 5.1, P = 0.004) was higher in cows negative for subclinical endometritis at week 8 postpartum and the proportion of cows that required more than 3 services was higher in cows with uterine inflammation. Also the proportion of cows diagnosed pregnant within 180 DIM was higher in cows with normal uterus at both week 4 (OR = 10.3, P = 0.001) and week 8(OR = 21.8, P = 0.001). These results indicated that subclinical endometritis was directly associated with poor body condition and subclinical mastitis and that it had negative effect on reproductive traits of dairy cows. This association may also reflect the possibility of translocation of bacteria/bacterial products from the uterus to the udder or vic-versa or else the presence of common cause for both endometritis and mastitis.     

Effects of work on reproductive and productive performance of crossbred dairy cows in the Ethiopian highlands

Summary An investigation was made at the International Livestock Centre for Africa (ILCA), into the possibility of using cows in land cultivation as a means of reducing the dependency of smallholder farmers in the Ethiopian highlands on draught oxen power, a resource which is in short supply during the peak of the cultivation season and usually leads to late planting and poor harvest. A total of 32 crossbred cows (1/2 Boran −1/2 Friesian) were used in an experiment to determine whether cows could be used to cultivate an average smallholder farm of 2·5 ha and to assess the effects of work on reproductive and productive performance; 16 served as a control group and were milked, but not worked while the other 16 were milked in addition to providing draught power for cultivation. Draught cows were provided with extra feed and consumed 7% and 21% more hay and concentrate respectively than non-draught cows during a two-lactation cycle. After the end of the second lactation there were no significant differences between draught and non-draught animals for milk production (1,713±57·4 compared with [vs] 1,857±48·1 kg), lactation length (291±20·4 vs 277±18·0 days), calf birth weight (29·6±1·0 vs 29·3±1·0 kg), number of days open (77±14·1 vs 83±12·9), calving interval (355±14·5 vs 358±13·2 days), gestation length (278±1·6 vs 274±1·4 days) and number of services per conception (1·21 vs 1·64). The number of hours worked by each pair of crossbred cows was sufficient to cultivate the average smallholder farm of 2·5 ha. However, the work done was spread over a longer time than that required by the smallholder farmer to cultivate 2·5 ha. It was concluded that at low levels of work and with improved feeding management, draught or traction does not have adverse effects on reproductive and productive performance of crossbred dairy cows.

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Resumen Se realizó una investigación en el Centro Internacional de Ganadería para Africa (ILCA), sobre el uso de vacas en el cultivo de la tierra en lugar de bueyes, los cuales son escasos en la época pico de labranza, lo cual conlleva a que se siembre tarde con la consecuente baja producción. Se utilizaron para el estudio 32 vacas media sangre Borán/Holstein, para determinar si éstas podían servir para las labores de cultivo de peque?as fincas de 2·5 hectáreas, sin menoscabo de la producción y reproducción. Dieciseis sirvieron como controles, las que se orde?aron pero no se utilizaron en labores de cultivo. Las vacas que se utilizaron para trabajar, recibieron alimentación extra, consumiendo 7% y 21% más heno y concentrado, durante dos ciclos de lactación.

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Résumé Une enquête a été réalisée à l'ILCA/CIPEA sur la possibilité d'utiliser des vaches pour cultiver la terre, en vue de réduire, la dépendance des petits fermiers des Hautes Terres éthiopiennes vis à vis des disponibilités en boeufs de trait. Cette ressource est en effet limitée pendant la pointe de la saison des cultures, et ceci a pour conséquences des plantations tardives et une moisson médiocre. Un total de 32 vaches croisées (1/2 Boran −1/2 Frison) ont été utilisées pour essayer de déterminer si ces animaux pouvaient être employés pour les travaux de cultures sur une ferme moyenne de 2,5 ha de superficie représentative d'une petite propriété et pour mesurer les effects du travail sur les performances de production laitière et de reproduction. Seize ont constitué un lot témoin. Elles ont été traites mais, n'ont pas travaillé tandis que 16 autres ont été traites tout en apportant leur force de travail pour la culture. Les vaches de trait ont re?u une alimentation complémentaire et ont respectivement consommé 7% et 21% de foin et de concentré de plus que les vaches non utilisées pour la traction pendant un cycle de 2 lactations.

     

The effects of calcium,phosphorus and zinc supplementation on reproductive performance of crossbred dairy cows in Tanzania

The effects of calcium (Ca), phosphorus (P) and zinc (Zn) supplementation on reproductive performance of grazing dairy cows was studied. Forty-eight cows in their first to third parity were allocated to eight groups of 6 animals each, based on stage of lactation and milk yield. Groups 1 (control), 2 (Ca), 3 (P) and 4 (Zn) received, respectively, no mineral supplement, 10 g Ca, 8 g P and 400 mg Zn. The rest of the groups received a combination of Ca/P, Ca/Zn, P/Zn or Ca/P/Zn. Animals were drenched daily. Ovarian activity was determined by progesterone concentrations in milk. Prepartum body condition score (BCS) measured using scale 1–5 was 2.5–3.5. Reproductive problems were observed in all groups except that supplemented with Ca. Cows supplemented with Ca, P, Ca/P, Ca/Zn and Ca/P/Zn had significantly (p < 0.05) shorter interval (30 days) from calving to resumption of oestrus as compared to control (69 days). Intervals from calving to conception and between calvings did not differ significantly between groups (p > 0.05), but were shorter in Ca-supplemented cows. Furthermore, cows in groups 2 and 3 needed an average of 2 services per conception against 3 for cows in other groups. Hence, supplementation with Ca, P and Zn of deficient dairy cows appears to improve reproductive performance.     

Reproductive performance of Holstein dairy cows in Iran

The objectives of the present study were to describe the current reproductive parameters of Holstein dairy cows in Iran and to determine factors which have a significant effect on reproductive performance with emphasis on high-producing dairy cows. Five large Holstein dairy herds from the major milk production areas of Iran were selected for this study. Reproduction data including parity of dam, calving date, days to first service, days open, number of services, dry period, and occurrence of diseases for cows that calved from 2004 to 2007 were collected from the herds' databases. To determine the effects of year and season of calving, disease status, level of milk production, and parity of dam on reproductive parameters, the proc-mixed procedure in SAS software was used. Overall, data about 8,204 lactation were collected for the study. Results showed that mean (±SD) days open, calving interval, and days to first service for study herds were 134 (±89), 403 (±86), and 67 (±38) days, respectively. Conception rates at the first service and the overall service-conception rate were 41.6% and 41%, respectively. The level of milk production and diseases had significant negative effects on days open and service per conception (P < 0.05); statistical analysis showed that for every 100-kg increase in milk yield, days open will increase by about 0.3 days. However, no significant effect of level of productivity was observed on days to first service. The results of this study indicate that high milk production is a risk factor for decreasing fertility in Iran, like many other parts of the world.     

Effect of timing of artificial insemination after synchronization of ovulation on reproductive performance in Holstein dairy cows

The objective of this study was to determine the effect of timing of artificial insemination on pregnancy rates, calving rates, abortion rates, twinning rates, and calf gender ratio after synchronization of ovulation with Ovsynch protocol in Holstein dairy cows. The ovulation of 219 lactating Holstein dairy cows was synchronized using the Ovsynch protocol. Therefore, cows received an injection of GnRH followed by an injection of prostaglandin F_2α 7 days later and a second treatment with GnRH 2 days later. Cows were artificially inseminated at 0, 12, or 24 h after the second injection of GnRH. Reproductive performance did not differ between cows inseminated at 0 h (n?=?82), 12 h (n?=?66), or 24 h (n?=?71) after the last injection of GnRH (pregnancy rate: 0 h 48 %, 12 h 47 %, 24 h 52 %; abortion rate: 0 h 5 %, 12 h 0 %, 24 h 11 %; calving rate: 0 h 43 %, 12 h 47 %, 24 h 41 %; twinning rate: 0 h 2 %, 12 h 0 %, 24 h 0 %; calf gender ratio (F/M): 0 h 61:39 %, 12 h 48:52 %, 24 h 39:61 %; P?>?0.05). Pregnancy rates for cows inseminated in postpartum times of 50–75, 76–100, and >100 days within the first and ≥3 parities were statistically similar (P?>?0.05), but pregnancy rates for cows inseminated at different postpartum times of 50–75, 76–100, and >100 days within the second parity were different (P?<?0.01). In general, pregnancy rates of cows inseminated at different postpartum times (P?<?0.01) and parities (P?<?0.001) differed. The findings of the current study showed that rates of pregnancy, abortion, calving, and twinning of Holstein dairy cows subjected to artificial insemination at different times after synchronization were similar. These results also indicate that the timing of artificial insemination after synchronization did not influence calf gender ratio. Furthermore, pregnancy rates of Holstein dairy cows inseminated after synchronization were significantly influenced by postpartum time and parity number.     

Effect of bypass fat supplementation on productive and reproductive performance in crossbred cows

Objectives of the present study were to evaluate the effects of supplementation of bypass fat on milk production and reproductive performance of crossbred cows. Nineteen multiparous crossbred cows (2–4 lactation) were divided in two groups on the basis of most probable production ability (MPPA). The animals in group 1 (nine cows, MPPA 3,441.32 kg, control group G1) were fed chaffed wheat straw, chopped green maize, and concentrate mixture as per requirements while the animals in group 2 (10 cows, MPPA 3,457.2 kg, treatment group G2) were fed the same ration supplemented with 2.5% bypass fat (on DMI basis). The cows of G2 were supplemented bypass fat 40 days prepartum to 90 days postpartum and carry over effect of supplementation on milk production and reproductive parameters was monitored up to 210 days of lactation. Average birth weights of the calves were 24.94 and 27.95 kg in G1 and G2, respectively. The calving per cent in G1 (88.88%) was lower than that of G2 (100%). The time taken for expulsion of fetal membranes was decreased (P < 0.05) by 5.4 h in G2 compared to G1. Days required for involution of uterus was less (P < 0.05) in G2 (35.40 days) than that of G1 (49.44 days). Less number of cases of retention of fetal membranes (RFM) and metritis were observed in G2 as compared to that of G1. The average milk yield (210 days) in G2 was higher (P < 0.05) than that of G1 (18.65 vs 17.57 kg/day). Similarly, the milk yield during the carry over period (90 days) was higher (P < 0.05) in G2 than that of G1 (14.81 vs 13.79 kg/day). The time required for onset of cyclicity was reduced (P < 0.05) by 6.5 days in G2 as compared to that of G1. The service period and AI per conception were also reduced (P < 0.05) in G2 while bypass fat feeding showed no effect on conception rate (P < 0.80). There were no differences between the two groups in plasma cholesterol, progesterone and insulin concentrations. Hence, it was concluded that bypass fat supplementation at 2.5% of DMI increased the milk production and reduced the time required for involution of uterus and commencement of cyclicity. AI per conception, incidences of metritis and RFM were also reduced on supplementing bypass fat.     

Effect of human chorionic gonadotropin on luteal function and reproductive performance of high-producing lactating Holstein dairy cows.

The objectives were to evaluate effects of human chorionic gonadotropin (hCG) (3,300 IU i.m.) administered on d 5 after AI on CL number, plasma progesterone concentration, conception rate, and pregnancy loss in high-producing dairy cows. Following the synchronization of estrus and AI, 406 cows were injected with either hCG or saline on d 5 after AI in a randomized complete block design. Blood sampling and ovarian ultrasonography were conducted once between d 11 and 16 after AI. Pregnancy diagnoses were performed on d 28 by ultrasonography and on d 45 and 90 after AI by rectal palpation. Treatment with hCG on d 5 resulted in 86.2% of the cows with more than one CL compared with 23.2% in controls. Plasma progesterone concentrations were increased by 5.0 ng/mL in hCG-treated cows. The presence of more than one CL increased progesterone concentration in hCG-treated cows but not in controls. Conception rates were higher for hCG-treated cows on d 28 (45.8 > 38.7%), 45 (40.4 > 36.3%), and 90 (38.4 > 31.9%) after AI. Treatment with hCG improved conception rate in cows losing body condition between AI and d 28 after Al. Pregnancy losses were similar between treatment groups. Treatment with hCG on d 5 after AI induces accessory CL, enhances plasma progesterone concentration, and improves conception rate of high-producing dairy cows.     

Effect of feeding on reproductive performance in Finnish dairy cows

The effect of 2 types of feeding on the involution of the genital tract and on the fertility was studied in 79 Finnish dairy cows on a research farm. The cows were fed twice a day with home-produced feed in accordance with the Finnish feeding standard. The cows were divided according to the type of feed into a hay-urea group and a silage group. The cows were examined clinically by rectal palpation 3 times a week during 8 weeks postpartum. The time required for the complete involution of uterus and cervix was recorded. The cows in the silage group had a significantly longer time in uterine involution, a lower fertility rate at first insemination and a longer interval from calving to conception than those in the hay-urea group. The pregnancy rate in the first insemination was in the hay-urea group 91% and in the silage group 57%. The interval between calving and the first insemination was shorter in the hay-urea group than in the silage group: 71.4 +/- 10.6 and 74.0 +/- 10.3 days, respectively. The interval between calving and conception was in the hay-urea group significantly (p less than 0.01) shorter than in the silage group; 74.8 +/- 15.1 and 89.5 +/- 24.4 days, respectively.     

Incorporation of estradiol benzoate to CIDR protocol improves the reproductive responses in crossbred dairy heifers

The present study was designed to determine the effect of estradiol benzoate (EB) on reproductive response following a controlled internal drug release (CIDR) protocol in crossbred (Sahiwal × Friesian) dairy heifers. In the first trial, a total of 100 crossbred dairy heifers were treated with CIDR protocol for 7 days and injected with the PGF_2α on day 6. After 24 h of CIDR removal, one group (EB?=?50) was injected with estradiol benzoate whereas the other (control?=?50) remained untreated. Estrus intensity and response were recorded visually and ovulation rate was recorded by ultrasonography. All heifers were artificially inseminated at 48 and 60 h following CIDR removal. Heifers were scanned for pregnancy within days 30–40 of artificial insemination (AI). In the second trial, two subgroups of heifers were included to observe the estrus and ovulatory events. The results of the first trial revealed that estrus response was achieved 100% in both the treatment groups. Estrus intensity (2.9?±?0.1 vs. 2.0?±?0.7) and ovulation rate (100 vs. 88%) differed significantly (P?<?0.05) between the EB and control groups. However, a tendency for higher pregnancy per AI was observed (54 vs. 36%; P?=?0.07) in EB than that in control groups. The results of the second trial revealed that a significantly (P?<?0.05) shorter estrus and earlier ovulatory events were observed in EB-treated heifers. It is concluded that the incorporation of estradiol benzoate to the CIDR protocol is helpful to improve the estrus signs and enhance the ovulation and the pregnancy per AI in crossbred dairy heifers.     

Influence of green grass-based diets on growth and reproductive performance in dairy heifers

Tropical Animal Health and Production - The objective of this study was to monitor the changes in growth, dry matter intake, and blood profiles (nutrition and reproductive hormones) of dairy...     

Effect of dystocia on subsequent reproductive performance and functional longevity in Holstein cows

The objective of this study was to evaluate the effect of dystocia on the reproductive performance and functional longevity in Iranian Holsteins. Data consisted of 1 467 064 lactation records of 581 421 Holstein cows from 3083 herds which were collected by the Animal Breeding Center of Iran from April 1987 to February 2014. Reproduction traits in this study included interval from first to second calving, days open and days from first calving to first service. The generalized linear model was used for the statistical analysis of reproductive traits. Survival analysis was performed using the Weibull proportional hazards models to analyse the impact of dystocia on functional longevity. The incidence of dystocia had an adverse effect on the reproductive performance of dairy cows. Therefore, reproductive traits deteriorated along with increase in dystocia score (p < 0.05). The culling risk was increased along with increase in the score of dystocia (p < 0.0001). The greatest culling risk was observed in primiparous cows, small herds and low‐yielding cows (p < 0.0001). Also, the lowest culling risk was found for cows calving at the youngest age (<27 months), and cows with age at first calving >33 months had the greatest risk (p < 0.0001). The results of current study indicated that dystocia had important negative effects on the reproductive performance and functional longevity in dairy cows, and it should be avoided as much as possible to provide a good perspective in the scope of economic and animal welfare issues in dairy herds.     

杂交荷斯坦母牛与其纯种在产奶、繁殖及抗病性状上的综合对比

为了提高荷斯坦奶牛的繁殖力,改善乳成分,增加其乳肉综合经济效益,本试验以蒙贝利亚乳肉兼用牛为父本,荷斯坦牛为母本进行杂交。通过构建线性模型、拟合泌乳曲线、计算综合经济效益等对其F1代母牛(69头)与荷斯坦纯种母牛(74头)的产奶性状、繁殖性状、抗乳房炎能力及综合经济效益进行了对比研究。结果如下:在产奶性能方面,蒙荷F1母牛乳脂率(3.59比3.49,P0.05)和乳蛋白率(3.25比3.12)(P0.01)显著高于荷斯坦母牛,而体细胞评分(2.37比2.85,P0.05)显著低于荷斯坦母牛;在饲料转化效率方面,泌乳盛期蒙荷F1母牛ECM/DMI(1.92比1.86,P0.01)极显著高于荷斯坦母牛;在繁殖性能方面,蒙荷F1母牛的初产月龄(25.38比26.33,P0.05)和空怀天数(87.35比107.16,P0.01)显著低于荷斯坦母牛;在综合经济效益方面,蒙荷F1母牛第1胎次泌乳期305d经济效益比荷斯坦母牛提高了4 918.15元。总之,乳肉兼用型的蒙荷杂种牛较荷斯坦母牛具有高乳脂率、高乳蛋白率,抗乳房炎能力强、投产早、空怀期短、综合经济效益高的优点。     

Effects of prostaglandin on the reproductive performance of dairy cows

A single injection of a synthetic analogue of prostaglandin F2 alpha (fenprostalene; Syntex) on the day of calving or between days 14 and 21 after calving did not affect the calving to first service interval, the number of services per conception or the conception rate of dairy cows. In a second trial, cows calved more than 45 days were injected once weekly with prostaglandin F2 alpha (dinoprost; Upjohn) or fenprostalene until served at the first detected oestrus. The calving to first service interval and the conception rate were not affected. Following injection of either prostaglandin, the spread in the pattern of onset of oestrus and the range in the proportion of cows (75 to 98 per cent) seen in oestrus within seven days were similar. This variation in the time of onset of oestrus after the administration of prostaglandin precludes limiting oestrus detection to four or five days per week, and is a major limitation to the use of prostaglandins in breeding programmes in dairy cows.     

日粮添加碳酸氢钠对荷斯坦奶牛生产性能的影响

选择体重、胎次、泌乳期、乳脂率和产奶量基本一致的健康无病的中国荷斯坦奶牛30头,随机分成3组,分别为试验组Ⅰ,Ⅱ和对照组。试验组Ⅰ,Ⅱ奶牛日粮每日每头分别添加130、150g碳酸氢钠,对照组奶牛日粮每日每头分别添加110g碳酸氢钠,试验期28d。结果表明,试验组Ⅰ干物质采食量、粪便pH比对照组高1.41%、0.20(P0.05),非脂乳固体比对照组低0.4(P0.05);试验组Ⅱ干物质采食量、产奶量、4%标准乳、粪便pH分别比对照组高2.04%、2.01%、2.68%、0.42(P0.05),乳脂率高0.13%(P0.05),乳蛋白、非乳脂固体分别低0.36%、0.51%(P0.05)。另外,碳酸氢钠的增加使得牛乳中体细胞数显著降低,且与乳脂肪呈显著负相关(P0.05),而与乳蛋白质呈显著正相关(P0.05)。由此可知,在每头奶牛日粮中添加150g碳酸氢钠的范围内,随着日粮中碳酸氢钠的增加,能显著改善荷斯坦奶牛的生产性能,有效预防奶牛瘤胃酸中毒。     

Milk yield and reproductive performance of brucellosis-vaccinated but seropositive Holstein cows

The aim of this research was to study if seropositivity for brucellosis in vaccinated cows against this disease hampers reproductive performance and milk production in high-yielding Holstein cows. For this purpose 1,026 healthy cows and 372 cows seropositive for brucellosis were enrolled in this study. Cows positive to card test and subsequently to the rivanol test were further subjected to the radial immunodiffusion (RID) test. It was found that only 11 % of the presumably infected cows by brucellosis screening tests were really infected with this disease. The reproductive performance of the group of cows with 11 % Brucella-infected animals was not impaired; overall pregnancy rate did not differ between seropositive and healthy cows (30.9 vs. 29.6 %). The abortion rates were similar between seropositive cows (5.3 %) and seronegative animals (6.9 %). Cows in the herd with 11 % Brucella-infected animals produced significantly more milk than unaffected cows over a 305-day lactation (10,684?±?1,720 vs. 10,345?±?1,736; mean ± SD; P?<?0.05). It was concluded that in dairy herds vaccinated against brucellosis with both 19 and RB51 strains, supplemental tests such as RID need to be conducted on all reactors in order to maintain diagnostic accuracy. These results also indicate that 11 % animal prevalence of brucellosis did not exert a detrimental effect on 305-day milk yield and reproductive performance in high milk-yielding Holstein cows.     

Effects of clinical mastitis on reproductive and milk performance of Holstein cows in Morocco

The aim of this study was to determine the influence of clinical mastitis and time of first mastitis occurrence on reproductive and milk performance of Holstein cows. Data were collected in a dairy farm from 2008 to 2012 on 1725 cows, among which 464 cows with mastitis. To determine the influence of clinical mastitis on reproductive and milk performance, models included fixed effects of parity, calving season, calving year, and group (cows with and with no mastitis). To determine the effect of time of 1st mastitis occurrence on reproductive performance, the mastitic cows group was further reclassified into three groups: prior to 60 days, between 60 and 90 days and greater than 90 days postpartum. For milk performance, the mastitic cows group was divided into two groups: before and after peak milk yield. Clinical mastitis had significant effects on calving to first AI interval, milk yield, and fat yield, but a non-significant effect on days open, number of inseminations per conception, and milk fat percentage. Mastitic cows had a calving to first AI interval 6.1 days longer and 549.6 kg milk and 20.4 kg fat per 305 days of lactation lower than those with no mastitis. Time of 1st mastitis occurrence did not have any significant effect on reproductive performance. Further, milk and fat yields of cows diseased before peak milk yield were 506 kg and 23.9 kg, respectively, lower than those of cows affected after peak milk yield. Extra attention needs to be paid to mastitis during the early postpartum period.

     

Serum levels of stanniocalcin-1 in Holstein heifers and cows

Stanniocalcin-1 is a hormone that possesses both paracrine and endocrine functions and has recently been identified in mammals. While paracrine functions have been determined for several organs, the role of circulating stanniocalcin-1 in cattle is still unclear but, observations in mice and cows suggest that stanniocalcin-1 plays a role in both gestation and lactation. The changes in serum stanniocalcin-1 content in different physiological states have never been evaluated in ruminants. We measured stanniocalcin-1 levels in sera from cattle ranging in age from post-weaned calves to 17-month-old heifers and in sera from cows during lactation and pregnancy. Our results indicate that the blood concentration of stanniocalcin-1 is increased by pregnancy, but not by lactation. The highest levels of stanniocalcin-1 were found in young calves and during the non-lactating period preceding calving. This suggests that stanniocalcin-1 is important for gestation and the preparation of the mammary gland for lactation.     

Seasonality in resumption of ovarian activity and reproductive performance of postpartum Holstein cows

It has been suggested that domestication has turned cattle from seasonal breeders to annual breeders. This study examined the seasonal differences in early postpartum ovulation and subsequent reproductive performance in 542 Holstein cows. Cows displaying corpora lutea in the ovary at 26 days postpartum were defined as early ovulators. Factors affecting the occurrence of early ovulation were analyzed, and subsequent reproductive traits were compared between cows with and without early ovulation. During the summer season, 70.6% of calving cows showed early ovulation, whereas 48.7, 39.2, and 47.2% presented this condition in autumn, winter, and spring, respectively (P < 0.01). Third parity cows showed early ovulation more often than their first parity counterparts (P < 0.05). Cows with a 2.50 to 3.00 or > 3.00 body condition score (BCS) more frequently became early ovulators than those with BCSs < 2.50 (P < 0.01). Calving year was a risk factor, and uterine abnormalities were also often risk factors for early ovulation. The survival analysis showed that seasonal differences in the occurrence of early ovulation did not completely affect the time to first service and pregnancy. Proportional hazard regression analysis revealed that calving year, parity, and early ovulation were risk factors for the time to first service and that calving year was a risk factor for the time to pregnancy. In conclusion, domesticated dairy cows maintain seasonality in postpartum ovarian activity but not in subsequent fertility.