Reproductive performance of Montbeliard cows reared under subtropical environment: effects of heat stress and acclimatization duration

L Allouche, T Madani¹, M Mechmeche^2,3 and A Bouchemal²

Department of Biology and Animal Physiology. Faculty of Nature and Life Sciences. Ferhat Abbas Sétif 1 University. Sétif 19000, Algeria.
lyallouche@gmail.com
¹ Department of Agronomy, Faculty of Nature and Life Sciences, Ferhat Abbas Sétif 1 University, Sétif, Algeria.
² National Center for Artificial Insemination and Genetic Improvement. Haouche Erroussi, Birtouta, Algiers 16045, Algeria.
³ Veterinary practice. Guellal, Sétif 19000, Algeria.

Abstract

The current study aimed to evaluate the reproduction performance of some Montbeliard cows imported from France and reared under subtropical Algerian environment. The reproduction parameters were recorded from 98 multiparous Montbeliard cows; 68 were pregnant after artificial insemination. However, gestation length, calf sex frequencies and calving types were recorded from 51 cows to investigate the effect of heat stress (summer vs fall) and the duration of the  cows in Algeria after import (36 cows <12 vs 32 ≥ 12 months).  No effect of heat stress was observed on all fertility parameters of Montbeliard cows, whereas fecundity parameters seemed to be altered. Montbeliard cows reared under subtropical environment conditions exhibited long calving-conception interval (Ca-CI) of 130 ± 64 days and calving-calving interval (Ca-CaI) of 404 ± 62 days. Hence, Ca-CI were longer in summer than in fall (139 ± 54 vs 112 ± 77 days; p=0.03), and among cows reared in subtropical environment for a period <12 months than those reared for a period ≥ 12 months (145 ± 52 vs 112 ± 72 days; p=0.03). Nevertheless, Ca-CaI was notably longer among cows reared for a period < 12 months than those reared for a period ≥ 12 months (420 ± 52 vs 380 ± 66 days; p=0.02). Also, heat stress or duration had no effect on calf sex (56.3 % females vs 43.8 % males). Most calvings of Montbeliard cows were easy (93.8 %). In conclusion, fecundity parameters of Montbeliard cows imported from France, introduced recently for breeding in subtropical environment, were affected by  summer heat stress mainly during the first year; hence, they require more attention for heat detection which can alleviate the reproductive problems.

Keywords: adaptation, ancientness, Algeria, fertility, fecundity, imported cow, summer

Introduction

Global warming has increased the surface temperature about 0.7°C since the early 20th century. It is virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales, as global mean surface temperature increases (IPCC 2014). In fact, the dairy industry is more susceptible to global warming. Heat stress in hot environments is one of the major factors that can negatively affect the milk production, the reproduction, and the health of dairy cows (El-Tarabany and El-Tarabany 2015). In a warm climate, this heat has to be dissipated if the thermal neutrality, a prerequisite for normal physiological function, is to be maintained. This complex interplay of physical and environmental effects influences the physiological functions of the cow and affects not only milk production but also the efficiency and profitability of the dairy enterprises (Kadzere et al 2002). The basic thermoregulatory strategy of a mammal is to maintain a body core temperature higher than the ambient temperature to allow the heat to flow out from the body via 4 basic routes of heat exchange: conduction, convection, radiation, and evaporation (Collier et al 2006).

Accurate measurement of when cows enter heat stress is complicated because the responses to heat stress affect not only the energy balance, but also water, sodium, potassium and chlorine metabolism. Water, sodium, potassium and chlorine are important constituents of sweat, and sweating is a major, if not the most important, thermoregulatory mechanism used to dissipate the excess body heat (Kadzere et al 2002). In Algeria, the state has advocated to import cows of high genetic potential and semen from France, Autstria and Canada to produce more and high quality of milk to satisfy consumer needs. Among the imported pure breeds, there are Montbeliard, Fleckvieh and Holsteins breeds. The Montbeliard breed belongs to the Jurassic branch which the group of Pie Rouge breeds stems from; it therefore belongs to the Simmental and Fleckvieh families. It is now the second dairy breed in France. The Montbeliard cow, a dual purpose breed, produces a milk highly appreciated by the cheese industry.

Moreover, the liveweight of Montbeliard adult cows and of young bulls varies from 650 to 750 kg depending on the age of slaughter (OS 2008). However, as meat has an attractive price compared to milk, Algerian farmers prefer to raise Montbeliard cows to produce mainly the veal; they also judge that Montbeliard breed has a good hardiness and adaptability to our hard  conditions compared to other breeds such as Holstein. Hence the purpose of the current study was to evaluate the reproduction performance of Montbeliard cows, imported from France and reared under subtropical Algerian environment conditions and to investigate the effects of summer heat stress and exxposure under these conditions. No study until now reported the effects of heat stress and length of exposure to subtropical environment on reproductive performance of Montbeliard cows.

Material and methods

Animals and management

In the current study, animal care protocol and all procedures used were approved by the Algerian animal welfare laws and policies (law 88-08, article 58).

The reproductive performance data of 98 multiparous Montbeliard cows were recorded between 1^st June and 30^th November 2012, reared mostly by smallholder farmers (<10 cows/farm) where the breeders adopt a similar feeding and management and the animals were raised under subtropical environment conditions in Setif (North East, Algeria). The meteorological data during our investigation are presented in Table 1. The data were collected from the weather station of Sfiha (Setif, Algeria), located at 36.18° latitude, 5.25° longitude and 1033 meters of altitude. The distance between the weather station and the dairy cattle farms is about 15 to 20 km. However, the temperature humidity index (THI) is a single value representing the combined effects of air temperature and humidity associated with the level of thermal stress. The THI was calculated following the formula indicated by NRC (1971).

THI = (1.8 × T_db+32) – [(0.55-0.0055 × RH) × (1.8×T_db-26.8)].

T_db = dry bulb temperature (°C), and RH = relative humidity (%).

The cows were aged 4.0 ± 1.5 years and had a mean body condition score (BCS) of 3.0 ± 0.50; the BCS was assessed using 1 to 5 scores (1: thin, 5: fat; Edmonson et al 1989). During summer and fall, the cows received a mixed ration containing wheat straws, grass corn, grass legumes and commercial concentrate and they had access to water two to three times by day depending on the heat.

In Algeria, the cows are often imported from their native countries when they are pregnant at about 7 months of pregnancy to calve here in Algeria. However, in our study two groups were considered for the duration of their livestock under Algerian subtropical environment, 36 cows who were reared for a period <12 months and 32 who were reared for a period ≥ 12 months in Algeria.

Reproduction performance

The cows were inseminated after visual heat-detection with frozen semen of 4 proven fertility Montbeliard bulls. Among them, 68 were diagnosed as pregnant via rectal palpation at around 10 weeks after artificial insemination (AI). Fertility and fecundity parameters were assessed according to Vallet (1997). For the fertility, the following parameters were evaluated: pregnancy rate (%) after 1, 2 and 3 AI, overall pregnancy rate (%), number of AI per conception. However, fecundity was assessed according to calving-conception interval (Ca-CI), frequency of Ca-CI >110 and calving-calving interval (Ca-CaI).

In addition, the following data were recorded for 51 cows after calving and analysed for 48 cows:

Gestation length, calf sex frequencies, and calving types, measured using 5 scores (1: unassisted, 5: caesarean section).

Statistical analysis

All data are presented as mean ± SD or as frequencies. Pregnant rates, frequencies of calving type and calf sex were compared between both group of seasons (summer vs fall) or livestock duration in Algeria (<12 vs ≥ 12 months), using Khi-square test or Fisher’s exact test when sample size was small. As small size was recorded in pregnant cows after ≥ three AI, they were grouped with those pregnant after two AI. Cows calving twins were excluded from the analysis. The comparison of data means of all variables between the previous groups was performed using Student test when variances were equal, or Mann–Whitney U test when variances were unequal. The homogeneity of variances was examined by the test of Levene’s test. The significance level was set at p <0.05. Statistical analysis was performed with SPSS 21 package program.

Results

Reproductive performance and effects of heat stress or duration of livestock under subtropical environment (<12 vs ≥ 12 months)

Fertility and fecundity parameters of Montbeliard cows are presented in Table 2. Overall pregnant rate was 69.0% and high frequency of pregnant cows was observed after the first AI (77.9%). Concerning fecundity parameters, Ca-CI was 130 days ± 64 and most of cows (62.0 %) had Ca-CI >110 days. The average of Ca-CaI was 404 days ± 62. All fertility parameters were similar (p>0.05) between seasons of summer and fall (Table 3); while, Ca-CI was longer (P=0.03) in summer (139 days ± 54) than in fall (112 days ± 77). Frequency of cows who exihibited Ca-CI >110 days, was higher (p=0.01) by 31 points in summer than in fall (72.7 % vs 41.7 %); while, Ca-CaI remain similar between both seasons (p >0.05).

However, no significance difference was observed in all pregnancy rates or in the number of AI/conceptions, between cows who reared in Algeria for a period <12 months and those who reared for a period ≥ 12 months (Table 4); whereas, Ca-CI was longer (P<0.03) among cows who reared for a period <12 months than those who reared for a period ≥ 12 months (145.22 days ± 52,0 vs 111.84 days ± 12,75). Hence, cows reared for a period <12 months had Ca-CI >110 days higher (p <0.001) by 40 points than those who reared for a period ≥ 12 months (80.6 % vs 40.6%).

Gestation length, calving type, calf sex and effect of heat stress or duration of livestock in Algeria

The length gestation was 280 ± 12 days (n = 48). An easy calving was noted in most of the Montbeliard cows (93.8 %). Frequency of male calves was similar to the frequency of the females (48.1 % vs 50.1%) (Table 5). No effect of heat stress or duration of livestock was observed on gestation length, calving type or calf sex (Table 6).

Discussion

The present data were the reproductive performance of 98 Montbeliard cows, imported from France and reared under subtropical climate in Setif (North East, Algeria) where dairy cattle are mostly present as smallholder farmers. In the current study, THI reach the extreme values in summer (100 to 101) compared to the values recorded in fall (74 to 92); such extreme values of THI were recorded in Egyptian subtropical environment (El-Tarabany and Nasr 2015). It was reported that if THI is above 82, the heat stress vulnerable cows may cease to produce or decline productivity, or even death may occur from heat stress (Du Prezz el al 1990).

Fertility and effect of heat-stress and duration of livestock

The fertility parameters recorded are within the standards values recommended by Vallet (1997), except the overall pregnancy rate which was low due probably to the short period of our investigation. Obviously, using a high quality of semen quality for AI improve fertility and increase genetic gain as indicated by several studies (IAEA 2007; Thibier 2005; Dahlen et al 2015). Moreover, using AI during summer avoids the negative effects of heat stress on bull performance on dairies (Collier et al 2006). Nevertheless, a high overall pregnancy rate (98%) was recently reported, when Montbeliard cows were crossed with a Belgian Blue-White breed bull in Setif (Algeria) and the animals reared under the same livestock conditions (Allouche et al 2016). However, the pregnancy rates observed in our investigation after 1, 2 and 3 AI recorded were better in Montbeliard cows reared under difficult conditions than those reported in Montbeliard cows reared in Ireland (Dillon et al 2003). In France, 19% of Montbeliard cows require ≥ 3 AI during 2008 (Le Mezec et al (2010); the high pregnancy rates observed after AI in our study were due probably to the long Ca-CI recorded as investigated by Friggens and Labouriau (2010).

In our research work, no effect of heat stress was observed neither on pregnancy rates nor on the number of AI/conception in Montbeliard cows. Previous American and Canadian studies reported that frequencies of non-return rates were highest in late summer and fall (Murray et al 1983; Taylor et al 1985); the conception risk of cows inseminated with frozen-thawed semen is negatively affected by long-term heat stress (Schüller et al 2016). Indeed, climate factors affected the conception rate of high producing dairy cows in Northeastern Spain (García-Ispierto et al 2007). Interesting, the fertility parameters in our study were similar between cows who were introduced recently in our farm and reared under subtropical climate for a period less than one year and those who reared for a superior period. No study in the word reported the effect of duration of livestock under subtropical conditions on reproductive performance of Montbeliard cows.

Fecundity parameters and effect of heat stress or duration of livestock

The Montbeliard cows reared under subtropical conditions had a long Ca-CI, longer in summer than in fall and among cows reared for a period less than one year than those reared for a period more than one year. Most of the Montbeliard cows had Ca-CI >110 days, frequencies were higher in summer than in fall by 31 points and among cows reared for a period < 12 months by 40 points than those reared for a period ≥ 12 months. Moreover, the Ca-CaI was longer notably among cows reared for a period ≥ 12 months than those reared for a period ≥ 12 months. All fecundity parameters were outside of the recommended norms; the Montbeliard cows reared in Morocco or in Ireland have a shorter Ca-CaI and Ca-CI (Dillon et al 2003; Boujenane and Aïssa 2008) than those noted in our study. Granaci and Morari-Pîrlog (2012) reported that the longest service-period for lack Spotted breed cattle in Moldova was recorded in the autumn months and the lowest results have been recorded in the spring-summer period.

Our results reveal that fecundity parameters of Montbeliard cows imported from France were affected by heat summer stress mainly during the first year of their introducing in Algeria, where temperature in summer reached 45°C and THI 101. Hence, cows will be face to hard breeding conditions, young cows were not yet be adapted to high temperature. If ambient conditions exceed body temperature, heat flow will reverse and the animal becomes a heat sink (Collier et al 2006); that consequently prolongs Ca-CaI and Ca-CI, due probably to the poor quality nutrition and heat silent which is frequent in summer (Thatcher et al 1986; Roelofs et al 2010). Although, it was reported that Holsteins in estrus during the summer had 4.5 mounts per estrus versus 8.6 for those in winter (Nebel et al 1997); thus ovaries take longer in dry season to resume ovarian activity because of the lower availability of forage in the pasture (Calderón-Robles et al 2011); hence, heat stress can cause a decrease in the intensity and expression of overt estrus and reduction in appetite and dry matter intake, as well as decrease the quality of oocyte and embryo by some endocrine changes and had a direct effect on gametes, embryo, and early fetus (Badinga et al 1993; Younas et al 1993; De Rensis and Scaramuzzi 2003; De Rensis et al 2015), which implies a longer calving interval and days open. Also, the summer heat stress lowered the in vitro embryo production of Holstein cows and heifers and enhanced the fragmentation rate of repeat breeder blastocysts (Ferreira et al 2011).

Our results show that cows exhibited a shorter Ca-CaI and Ca-CI after one year of livestock in Algeria which could be explained by their adaptability and tolerance after this period to the high temperature and hard breeding conditions. The Montbeliard cows were known by their good feet and legs (Paulson et al 2015), that’s why our farmers prefer to raise these cows than other breeds as Holstein cows. In fact, the adaptability of Montbeliard breed has been confirmed by results recorded during thermotolerance tests carried out on cattle by the INRA in 1975. It seems that rectal temperature varies very little in Montbeliard breed during periods of stress and the respiratory rhythm and sweating are less prone to change in Montbeliards than in Holsteins; this makes it easier for the breed to adapt to hot climates (OS 2008). However, extra heat has been accommodated by physiological adaptations (Kadzere et al 2002); skin surface temperature might be the physiological triggering mechanism for high rates of evaporation (Maia et al 2005). However, El-Tarabany and Nasr (2015) reported that Brown Swiss cows have a better reproductive performance and adaptability than pure Holstein under subtropical Egyptian condition, this breed was less sensitive to heat stress which might be attributed to their coat color. Brown Swiss had a light brown color which decreases the inward flow of heat than the black one (Finch 1986). Other breeds as buffalo, B. indicus and Zebu-type cattle seem more adapted to thermal stress than Bos taurus-type cattle (Mullick 1960; Kadzere et al 2002).

The ability to regulate temperature is an evolutionary adaptation that permits homeotherms to function in spite of variation in ambient temperature (Bitman et al 1984). If a rise in body temperature is to be avoided, the excess heat in the body must be dissipated to the environment by two routes: sensible (i.e. “dry” convective and thermal radiation) and latent heat (i.e. evaporation) transfer. Sensible heat losses from the body are governed by the temperature gradient and air velocity, while evaporative heat losses are controlled by the vapour pressure gradient (Maia et al 2005). It's clear that the high days open and Ca-CI affects farm economy during summer, consequently decrease profitability of farmers and dairy industry. In our current study, the Montbeliard cows required more attention to shorten Ca-CaI and Ca-CI, especially those imported recently from France. One of the factors that increase the Ca-CI of dairy cow during the hot season of the year is the poor detection of estrus. The use of tailhead paint, the HeatWatch system, radio-telemetric pressure transducers and pedometers can improve estrus detection and thus fertility. However, there are no published studies that have evaluated the effects of these aids to estrus detection on summer infertility (De Rensis and Scaramuzzi 2003). Recent studies discussed some hormonal treatments to solve better reproductive disorders related to a hot environment as use of gonadotropins to induce follicular development and ovulation, breeding synchronization protocols for fixed-time AI (FTAI) to inseminate without the need for estrus detection and the progesterone-based protocols, applied either for FTAI or after AI (De Rensis et al 2015). Also, using cooling systems in areas dairy operations seems to enhance cow comfort, improve milk production, reproductive efficiency, and profit (Collier et al 2006).

Gestation length, calving types and calves sex frequency and effect of heat stress or duration of livestock

However, length gestation in our study was close to that reported in Montbeliard cows in previous studies (Dillon et al 2003; Boujenane and Aïssa 2008). Most of Montbeliard cows reared under our subtropical conditions had easy calving; while, high incidence of difficult calving was noticed in pure Holstein heifers and cows reared under subtropical Egyptian conditions (El-Tarabany 2015). The frequency of male calves recorded was similar to the frequency of females. In Algeria, the Montbeliard cows are raised to produce primarily meat veal because it has an attractive price as explained previously in our research. In our study, gestation length, calving types and calf sex frequencies seem to be not affected by the seasons (summer vs fall) nor by the duration of livestock in the subtropical environment (<12 months vs ≥ 12 months).

Conclusion

• No effect of heat stress was observed on all fertility parameters of introduced Montbeliard cows, whereas fecundity parameters seemed to be altered.
  
  
• Our study highlighted that summer heat stress had a negative effect mainly on Montbeliard cows introduced recently for breeding in subtropical environment; therefore, these young cows require more attention for heat detection which can alleviate the reproductive problems.
  
  
• Cooling systems, using aids to estrus detection and hormonal treatments, seem appropriate to minimize days open and calving interval under heat stress allowing then more profitability for producers and reducing economic losses.

Acknowledgements

The authors acknowledge the inseminators: Arama L. Semecha R. and Sersoub L. and all farmers who noticed information for our investigation. Also, the support provided by the National Center for Artificial Insemination and Genetic Improvement (CNIAAG) of Algiers (Algeria) is gratefully acknowledged.

References

Allouche L, Madani T, Mechmeche M, Sersoub L and Bouchemal A 2016 Productive and reproductive performances of Montbeliarde cows crossed with a Belgian Blue-White breed bull in Algeria. Renc. Rech. Ruminants, 23. http://www.journees3r.fr/IMG/pdf/Texte_7_affiche_Reproduction_L-Allouche.pdf

Badinga L, Thatche W W, Diaz T, Drost M and Wolfenson D 1993 Effect of environmental heat stress on follicular development and steroidogenesis in lactating Holstein cows. Theriogenology 39, 797-810.

Bitman J A, Lefcourt D L and Stroud B 1984 Circadian and ultradian temperature rhythms of lactating dairy cows. Journal of Dairy Science 67, 1014-1023.

Boujenane I and Aïssa H 2008 Performance de reproduction et de production laitière des vaches de race Holstein et Montbéliarde au Maroc. Revue d'Elevage et de Médecine Vétérinaire des Pays Tropicaux 61, 191-196.

Collier R J, Dahl G E and Van Baale M J 2006 Major Advances Associated with Environmental Effects on Dairy Cattle. Journal of Dairy Science 89, 1244-1253.

Dahlen C, Black D and Crosswhite M 2015 Maximizing pregnancy rates when using artificial insemination. NDSU Extension Service. North Dakota State University, 8. Retrieved on 15 January 2017, from https://www.ag.ndsu.edu/pubs/ansci/livestoc/as1749.pdf

De Rensis F, Garcia-Ispierto I and López-Gatius F 2015 Seasonal heat stress: Clinical implications and hormone treatments for the fertility of dairy cows. Theriogenology 84, 659-666.

De Rensis F and Scaramuzzi R J 2003 Heat stress and seasonal effects on reproduction in the dairy cow-a review. Theriogenology 60, 1139-1151.

Dillon P, Snijders S, Buckley F, Harris B, O’Conn P and Mee J F 2003 A comparison of different dairy cow breeds on a seasonal grass-based system of milk production. 2. Reproduction and survival. Livestock Production Science 8, 35-42.

Du Preez J H, Hattingh P J, Giesecke W H and Eisenberg B E 1990 In Heat Stress and Animal Productivity. (ed. A Aggarwal and R Upadhyay), pp. 5. Springer Science & Business Media, New Delhi, IN.

El-Tarabany M S 2015 Effects of calving difficulty on the subsequent reproductive performance and milk production of Holstein, Brown Swiss and their crosses. Livestock Science 180, 263-267.

El-Tarabany M S and El-Tarabany A A 2015 Impact of maternal heat stress at insemination on the subsequent reproductive performance of Holstein, Brown Swiss, and their crosses. Theriogenology 84, 1523-1529.

El-Tarabany M S and Nasr M A F 2015 Reproductive performance of Brown Swiss, Holstein and their crosses under subtropical environmental conditions. Theriogenology 84, 559-565.

Ferreira R M, Ayres H, Chiaratt M R, Ferraz M L, Araújo A B, Rodrigues C A, Watanabe Y F, Vireque A A, Joaquim D C, Smith L C, Meirelles F V and Baruselli P S 2011 The low fertility of repeat-breeder cows during summer heat stress is related to a low oocyte competence to develop into blastocysts. Journal of Dairy Science 94, 2383-2392.

Finch VA 1986 Body temperature in beef cattle: its control and relevance to production in the tropics. Journal of Animal Science 62, 531-542.

Friggens N C and Labouriau R 2010 Probability of pregnancy as affected by oestrus number and days to first oestrus in dairy cows of three breeds and parities. . Animal Reproduction Science 118, 155-162.

García-Ispierto I, López-Gatius F, Bech-Sabat G, Santolaria P, Yániz JL, Nogareda C, De Rensis F and López-Béjar M 2007 Climate factors affecting conception rate of high producing dairy cows in northeastern Spain . Theriogenology 67, 1379-1385.

Granaci V and Morari-Pîrlog A 2012 Reproductive and Productive Indices of the Moldavian Black Spotted Breed Cattle Population of “South” Subtype. Bull. UASVM Anim.

Intergovernmental Panel on Climate Change (IPCC) 2014 Climate Change: Synthesis Report; Summary for Policymakers. Retrieved on 10 September 2017, from https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf.

International Atomic Energy Agency (IAEA) 2007 Improving the reproductive management of dairy cattle subjected to artificial insemination. IAEA-TECDOC-1533, 1-141. Retrieved on 28 April 2018, from http://www- pub.iaea.org/MTCD/publications/PDF/te_1533_web.pdf

Kadzere C T, Murphy M R, Silanikove N and Maltz E 2002 Heat stress in lactating dairy cows: a review. Livestock Production Science 77, 59-91.

Le Mezec P Barbat-Leterrier A Barbier S De Cremoux R Gion A and Ponsart C 2010 Fertilité et génétique : la réconciliation. Reproduction IA. Bulletin Technique de l’Insémination Animal 137, 29-32.

Maia A S, Da Silva R G and Battiston Loureiro C M 2005 Sensible and latent heat loss from the body surface of Holstein cows in a tropical environment. International Journal Biometeorology 50, 17-22.

Mullick D N 1960 Effect of humidity and exposure to sun on the pulse rate, respiration rate, rectal temperature and haemoglobin level in different sexes of cattle and buffalo. Journal of Agriculture Science 54, 391-402.

Murray B B, Scheffer L R and Burnside E B 1983 Heritability of nonreturn rate of Canadian Holstein Friesian bulls. Canadian Journal of Animal Science 63, 39-48.

National Research Council (NRC) 1971 A Guide to Environmental Research on Animals. National Academy of Sciences, Washington, DC, USA.

Organisme de sélection de la race Montbéliarde (OS) 2008 The Montbeliard breed. INRA, research station of Villers Bocage 1-4.

Paulson J, Salfer J, Newell S, Santi E, Seykora T, Litherland Y et al 2015 Learning about Dairy. University of Minnesota Extension, 11. Retrieved on 20 December 2017, from https://www.extension.umn.edu/youth/mn4-H/events/project-bowl/docs/PB-Learning-About-Dairy-Booklet.pdf

Roelofs J, López-Gatius F, Hunter R H, van Eerdenburg F J and Hanzen Ch 2010 When is a cow in estrus? Clinical and practical aspects. Theriogenology 74, 327-44.

Schüller L K, Burfeind O and Heuwieser W 2016 Effect of short- and long-term heat stress on the conception risk of dairy cows under natural service and artificial insemination breeding programs. Journal of Dairy Science 99, 2996-3002.

Taylor J F, Everett R W and Bean B 1985 Systematic environmental, direct, and service sire effects on conception rate in artificially inseminated Holstein cows. Journal of Dairy Science 68, 3004-3022.

Thatcher W W, Collier R J 1986 Effects of climate on bovine reproduction. In Current therapy in theriogenology (ed. DA Morrow), pp. 301-309. W.B. Saunders, Philadelphia.

Thibier M 2005 The zootechnical applications of biotechnology in animal reproduction: current methods and perspectives. Reproduction Nutrition Development 45, 235-242.

Vallet A 1997 La fécondité des troupeaux laitiers, un grand problème d'actualité. Bulletin Technique de l’Insémination Animale.

Younas M, Fuquay J W, Smith J A E and Moore A B 1993 Estrous and endocrine responses of lactating Holsteins to forced ventilation during summer. Journal of Dairy Science 76, 430-436.

Received 30 April 2018; Accepted 13 June 2018; Published 3 July 2018

Go to top