Thoroughbred foals' mortality causes during first six months of life. Part I. Effect of parents and prenatal factors

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1 Roczniki Naukowe Polskiego Towarzystwa Zootechnicznego, t. 5 (2009), nr 3 Thoroughbred foals' mortality causes during first six months of life. Part I. Effect of parents and prenatal factors Maria Kulisa, Katarzyna Makieła, Bogusława Długosz, Magdalena Gaj University of Agriculture in Kraków, Department of Horse Breeding, al. Mickiewicza 24/28, Kraków The aim of the study was to analyze the chosen factors affecting Thoroughbred foals' mortality during first six months of life. Data based on broodmare cards, foaling notes and direct information received from the generał farm manager were collected in one of Polish Thoroughbred National Studs. The breeding season, age of a broodmare, pregnancy length and stalli on used for breeding were considered. Data on 105 broodmares and 13 stallions were coilected. Only stallions with at least 10 progeny were considered. Twelve breeding seasons during which 395 foals were Iive-born, were analyzed. Foals were divided into two groups: dead foals until third day of life and dead foals from fourth day of life up to weaning (around six month of life). Considerable fiuctuations of foals' mortality rate during particular breeding seasons were stated. The highest number of foals was weaned from 4-7 years old mares and the lowest from 8-11 years old mothers. Choice of stallion for breeding had impact on foals' survival rate. It was noted that three of studied stallions had relatively high level of foals' mortality rate in the first three days of life. Pregnancy length affected the number of foals' deaths caused by prenatal factors. KEY WORDS: foals / mortality / Thoroughbred horses Compared to other breeds, Thoroughbred horses are distinctive for lower reproduction parameters. Slightly more than 50% of Thoroughbred mares bred each year mange to nurture foals that can be further used and bred [2, 5, 10, 11]. This may be due to lower fertility, developmental and functional disorders of mares' reproductive systems, various genetic defects, or poor-quality semen [3, 12]. The number of foals reaching the weaning age is also influenced by a relatively high percentage of twin pregnancies and a reduced foal immunity caused by a high inbred coefficient [7, 8]. Bosted [l] reports that deaths prior to weaning account for 5-15% of foals, which makes it so significant to increase delivery monitoring and develop preventive measures in foal care. 71

2 The aim of the study was to analyze the chosen factors affecting Thoroughbred foals' mortality during first six months of life. Materiał and methods Research subject included 395 foals bom at one of Polish National Thoroughbred Studs over 12 years. Data on 105 broodmares and 13 stallions were collected. Only stallions with at least 10 progeny were considered. The study focused on causes of foals' deaths, which were analyzed based on broodmare cards, foaling notes and direct information received from the general farm manager. The aim of the research was to find out whether factors such as the breeding season (I-XII), broodmare age, pregnancy length, stallion-sire (A-M) and prenatal factors had an influence on foals' mortality. Foals have been divided into two groups: dead foals until third day of life and dead foals from the fourth day of life up to weaning, that is, around the sixth month of life. Results and discussion Foals' mortality in particular seasons has been presented in Table 1. The highest percentage of dead foals until third day of life was noted for season I (13.79%) and season VIII (12.12%), whereas no deaths in this group have been recorded for seasons IV, V, VII, IX and X. Season VIII was also marked by the highest percentage of dead foals from the fourth day of life up to weaning, which was as high as 33.34%. In addition, high mortality was recorded in season X (27.03%). The highest number of foals was weaned in seasons IX (92.31 %), XI (91.18%) and IV (87.50%). The conducted research revealed that foals' mortality until the third day of life in particular years (seasons) oscillated between O and 13.79%, while from the fourth day of life up to weaning - between 7.96 and 33.34%. It can be assumed therefore that particular breeding seasons affected foals' mortality rate. The study also focused on the relationship between broodmare age and the number of dead foals. The mares were divided into four age groups (Table 2). Among broodmares aged 4-7 years old, no dead foals until third day of life were recorded, whereas dead foals from fourth day of life constituted only 3.45% (Table 3). Compared to the remaining age groups, it can be concluded that the number of foals reaching the weaning age was the highest for broodmares aged 4-7. The highest percentage of dead foals until third day of life (5.77%) and from the fourth day of life up to weaning (19.23%) was observed for broodmares aged 8-11 years old. Among thirteen stallions, with at least ten progeny, no dead foals until the third day of life were recorded in the case of six horses (A, B, C, D, G, J), while 100% of foals were weaned in the case of two stallions (A, D) - Table 4. Highest mortality rate until third day of life was noted for stallions F (15.79%), K (8.82%) and E (7.15%). Stallions C (27.27%), I (26.67%), and F (21.05%) were distinctive for highest mortality rate of dead foals from the fourth day of life. A very low percentage of foals sired by stallion F reached the weaning age (63.16%). It is therefore probabie that foals' mortality rate, 72

3 Table 1 - Tabela 1 Number and percentage of dead foals up to third day of life and from fourth day of life in analyzed breeding season Liczba i procent źrebiąt padłych do 3. dnia życia oraz od 4. dnia życia do odsadzenia w poszczególnych sezonach Number of Oead foals up Dead foals frorn Number of weaned Season live-bom to third day fourth day Total foals Sezon foals of life of life Razem Liczba źrebiąt Liczba Źrebięta padle Źrebięta padle odsadzonych źrebiąt do 3. dnia życia od 4. dnia życia żywo urodz. % n % n % n % n I! l 31 III IV 24 O O V 35 O O VI VI! 30 O O VlII II IX 26 O O X 37 O O XI U8 31 XII Total Ogółem Table 2 - Tabela 2 Number of broodmares in particular age groups Liczebność klaczy matek w poszczególnych grupach wiekowych Group Grupa Age groups n Przedzialy wiekowe I II III IV and more - 16 i więcej Tatal - Razem \05 73

4 Table 3 - Tabela 3 Number of percentage of de ad foals up to third day oflife and from fourth day oflife in p art icular age groups ofbroodmares Liczba i procent źrebiąt padłych do 3. dnia źyciai od 4. dnia źycia z uwzględnieniem grup wiekowych klaczy matek Broodmares' Number of Dead foals up Dead foals from Number of weaned, age groups live-born to third day foui1hday foals Grupy foals of life of life Total Liczba źrebiąt wiekowe Liczba Źrebięta padle Źrebięta padle Razem odsadzonych klaczy źrebiąt do 3. dnia życia od 4. dnia życia żywo urodz. n % n % n % n % 29 O O II III III IV Total Ogółem ~ j i Table 4 - Tabela 4 Number of percentage of dead foals up to third day of life and from fourth day of life sired by particular 1 stallions Liczba i procent źrebiąt padłych do 3. dnia życia i od 4. dnia życia z uwzględnieniem ogierów ojców. 1 Number of Dead foals up Dead foals frorn Number of weaned live-bom to third day fourth day foals Stallions foals of life of life Total Liczba źrebiąt Ogiery Liczba Źrebięta padle Źrebięta padle Razem odsadzon ych źrebiąt do 3. dnia życia od 4. dnia życia żywo urodz. n % n % n % n % A 10 O O O O O O B 11 O O C II O O l D 11 O O O O O O E 14 I II F G 25 O O H I 30 I J. 31" O O K L ; M Total Ogółem J ". 74

5 particularly until the third day of life (postpartum period), was inf1uenced by stallion which sired the foals. In the researched factors (Tab le 5). stud, 3.29% of foals died until the third day of life due to prenatal Hołda [6] points out anatomical defects, such as bladder rupture, limb deformation or rib fracture to be the most com mon and visible disorders in the first days of foal's life. He also mentions the Neonatal Maladjustment Syndrome, which occurs as a result of hypnoxia [6]. However, a certain number of unable to live newborn foals do not reveal any clinical symptoms. These frequently come from twin pregnancies where proper fetal development may be impaired. Kulisa et al. [7] report that for 8.5% of multiple pregnancies, both foals are stillborn or incapable of normai life. In the researched stud, smali and weak newborn foals which did not demonstrate a sucking ref1ex or did not catch breath were considered dead due to prenatal factors. In most cases, this was not c\early specified in broodmare cards. An attempt has also been made at investigating the relationship between pregnancy \ength and the num ber of dead foals up to weaning, with particular consideration for deaths as a result of prenatal factors. An average pregnancy, leading to a delivery of a healthy foal, which later reached the weaning age, lasted 336 days (Tab le 5). These results approximate numbers established by Detkens [4] for a single pregnancy of a Thoroughbred mare: days. Naróg-Bryzik [9] obtained a similar value in her studies: days. Dead foals until third day of life as a result of prenatal factors came from shortest pregnancies, lasting days in average. It was conc\uded that pregnancy length does not exert a significant influence on foal losses. Table 5 - Tabela 5 Average pregnancy length with number of live-born foals and number offoals which death was caused by prenatal factors taken into consideration Srednia dl ugość ciąży z uwzględnieniem liczby urodzonych źrebiąt i upadków na skutek czynników prenatalnych Foals Źrebięta n % Average pregnancy length (days) Średnia długość ciąży (dni) Dead up to third day of life Padle do 3. dnia życia preriatal factors czynniki prenatalne other inne Dead from fourth day of life Padle od 4. dnia życia ! Weaned - Odsadzone 3! Total - Razem =--==------== = ł..

6 A specific character of Thoroughbred breeding entails more serious, when com pared to other horse breeds. The study revealed considerable fluctuations of foals' mortality rate during particular breeding seasons. Within particular broodmare age groups, the highest percentage of foals was weaned from mares aged 4-7 years old. Largest losses were recorded among 8-11-year old mares, which should be taken into consideration when defining most favorable broodmare age structure in stud. A relati vely high perinatal mortality rate among foals sired by three of the studied stallions may suggest a relationship between the choice of stallion and survival rate among its foals. It was also conc1uded that pregnancy length affected the number of foals' deaths caused by prenatal factors. These foals came from the shortest pregnancies. Foals ' mortality rate may be therefore decreased by a more suitable choice of stallions and taking particular care of mares aged 8-11 years old. BIBLIOGRAPHY \. BOSTEDT H., Wybrane zagadnienia dotyczące opieki nad źrebiętami we wczesnym okresie po urodzeniu. Medycyna Weterynaryjna 47 (3), BYSZEWSKI W., GROMNICKA E., Wyniki rozrodu klaczy w Państwowych Stadninach Koni w latach Medycyna Weterynaryjna 50 (LO), CUNNINGHAM E.P., ALWAN S., BADAI A.M., O'BYRNE T.M., High levels of infertility in horses. Farm and Food Researclt 11 (2). 4. DETKENS S., Studia nad długością ciąży i próba określenia jej odziedziczalności u klaczy pełnej krwi angielskiej. Roczniki Nauk Rolniczych, t. 83-B-2, GERINGER H., HOŁOWKO K., Analiza rozrodu klaczy pełnej krwi angielskiej stadnin dolnośląskich w latach Zeszyty Naukowe Przegladu Hodowlanego 50, HOŁDA G., Poród. Świat Koni l (21), KULISA M., PIESZKA M., FRYBES O., Ciąże bliźniacze w hodowli koni pełnej krwi angielskiej w Polsce w latach Medycyna Weterynaryjna 55 (l O), MAX A., Niewydolność oddechowa i zapalenie płuc u źrebiąt. KOli Polski 2 (225), NARÓG-BRYZIK 1., Płodność a wyniki hodowlane koni pełnej krwi angielskiej w SK Moszna w latach Praca magisterska, AR Kraków. 10. OLEKSIAK S., Wyniki rozrodu w stadninach koni pełnej krwi angielskiej w latach Koń Polski 3 (91), 6-9. l\. OLEKSIAK S., Ocena wyników hodowlanych klaczy pełnej krwi angielskiej w polskiej hodowli w latach Sympozjum Międzynarodowe "Aktualne kierunki hodowli i użytkowania koni w Europie", Kraków, WIERZBOWSKI S., KOSINIAK-KAMYSZ K., Kierowany rozród koni. Drukrol, Kraków. 76

7 Maria Kulisa, Katarzyna Makieła, Bogusława Długosz, Magdalena Gaj Przyczyny śmiertelności źrebiąt pełnej krwi angielskiej w okresie pierwszych sześciu miesięcy życia. Cz. 1. Wpływ rodziców i czynników prenatalnych Streszczenie Celem badań była analiza wybranych czynników wpływających na śmiertelność źrebiąt pełnej krwi angielskiej w okresie pierwszych sześciu miesięcy życia. Dane uzyskano z kart klaczy matek, zeszytów porodowych oraz bezpośrednich informacji od dyrektora stadniny. Rozpatrywano: sezony, wiek klaczy matek, długość ciąży oraz wpływ ogierów użytych do rozrodu. Zebrano informacje na temat 105 klaczy i 13 ogierów, po których urodziło się co najmniej 10 źrebiąt. Przeanalizowano 12 sezonów rozrodczych, w których urodziło się 395 źrebiąt. Źrebięta padłe podzielono na grupy - do trzeciego dnia życia oraz od czwartego dnia po urodzeniu do odsadzenia, tj. do szóstego miesiąca. Stwierdzono duże wahania w ilości upadków źrebiąt w poszczególnych sezonach. Najwięcej źrebiąt w stosunku do urodzonych odsadzono od młodych matek w wieku 4-7 lat, zaś najmniej od klaczy 8-1 I-letnich. Dobór ojców do rozrodu wpływa! na przeżywalność źrebiąt. Zanotowano stosunkowo wysoką śmiertelność okołoporodową źrebiąt pochodzących po trzech spośród badanych ogierów. Stwierdzono wpływ długości ciąży na upadki źrebiąt z przyczyn prenatalnych. Źrebięta te pochodziły z najkrótszych ciąż. Ograniczenie liczby upadków źrebiąt można uzyskać poprzez bardziej odpowiedni dobór ogierów do rozpłodu oraz otoczenie szczególną opieką klaczy w wieku 8-11 lat. 77