| Livestock Research for Rural Development 22 (7) 2010 | Notes to Authors | LRRD Newsletter | Citation of this paper |
The ovaries of 1270 Bos indicus cows where used to evaluate the influence of breed on ovarian activity. Three breeds (Red Bororo, White Fulani and Wadara) were used. The presence or absence of pregnancy was noted after slaughter, and the ovaries were collected. Follicles were measured and classified as small (1 to 4mm), medium (5 to 8mm) or large (≥9mm) in diameter. Corpus luteum was classified as functional CL or corpus albicans based on gross morphology. Luteal structures and follicles were compared with different phases of the oestrus cycle. Based on this, the cows were classified as cycling, pregnant, anoestrus, prepubertal heifers or those having abnormal ovarian activity.
Difference in breed did not show effect on follicular population and development (P>0.05). Also prevalence of various functional states of ovaries did not reveal superiority of any breed over the others. It was concluded that the study did not detect any effect of breed on ovarian activity of Bos indicus cows.
Keywords: Abattorir, breed, follicles, pregnancy, reproduction
The major classes of domestic cattle in the world are the Bos taurus and Bos indicus (Payne 1990, Maule 1990). Bos taurus are the hump less temperate breeds found in Europe and North America which as a result of careful breeding and selection can produce higher yields of milk and beef (McDonald and Low 1985).They are characterized by high reproductive performance in which a calf attains puberty at one year and subsequently calves every year (Maule 1990). Bos indicus on the other hand are the humped zebu cattle indigenous to the tropical and subtropical regions of Africa, Asia and some parts of Australia. They are adapted to the tropical climate and are able to withstand greater heat and poorer diet than the temperate type. The breeds of zebu indigenous to Nigeria are White Fulani, Red Bororo, Shuwa (Wadara) and Sokoto Gudali (Payne 1990).
In the tropics, apart from the primary values of milk and beef production, cattle provide other products that are of value such as hides, used for leather work, dung used for fuel and fertilizer. Cattle are used extensively for drought purposes in many parts of Africa and Asia where they are employed in a variety of farm work such as transportation and lifting water. In many cattle owning tribes, cattle are regarded as a means of wealth and prestige and they serve as a means of fulfillment and a mark of respectability and status in the society (Payne 1990). The cyclical activity of the cow’s reproductive systems can be assessed from ovarian faction using follicular population and sizes and the presence of corpora lutea (Dominguez 1995).
Follicular development occurs in waves in cows with one dominant follicle which may reach maturity and ovulates or becomes atretic together with several other subordinate follicles of different, but smaller sizes depending on the stage of oestrus cycle in which there may be raised concentration of estrogen and gonadotropins or progesterone to stimulate or inhibit ovulation respectively (Fortune 1993). In a tropical country like Nigeria where over ninety percent of cattle are managed under extensive system, poor fertility is not an uncommon problem among the cattle herds. In addition to nutrition the harsh climatic conditions and poor management are other contributing factors to fertility problems in the tropic (Voh et al 1984).
This study was undertaken to evaluate the effect of breed on ovarian activity using different stages of follicular development and types of corpora lutea (active corpus luteum, corpus albicans and corpus luteum of pregnancy as indicators of ovarian function to determine whether breed differences exert effect on the ovarian parameters mention. Dominguez (1995) reported significantly more large follicles in European breeds (Bos taurus) than zebu cows (Bos indicus) and cross breed cows (Bos taurus x Bos indicus)
The study was conducted on cows slaughtered at the Maiduguri abattoir. The animals were indigenous to the geographical areas of the Sudan Savannah and Sahel Savannah (arid and to semi arid regions of northeastern Nigeria and neighboring parts of Niger, Chad and Cameroon Republics). The areas are characterized by low annual rainfall and sparse vegetation and the animals are generally kept under extensive management system.
Three breed of cows were used in this study namely Red Bororo, Wadara and White Fulani. A total of 1270 animals were studied. Each cow was examined before slaughter to identify its breed. After slaughter the reproduction organs of the cows was brought out. The presence or absence of pregnancy was noted, but examination for trimester of pregnancy was not made. The ovaries were then collected and tagged with labels indicating the serial number of the animals. The samples were then transported to the laboratory for examination.
The ovaries were trimmed of excessive connective tissue and washed with tap water. The total number of visible follicles on the surface of each ovary was counted, and the diameter of each follicle measured using vernier caliper. Follicles were classified into three size categories; small follicles (1to 4mm), medium follicles (5 to 8mm) and large follicles (≥9mm) (Dominguez 1995).
Lutuel structures were identified on the ovaries and each structure was classified as active corpus lutuem, corpus albicans or corpus lutuem of pregnancy based on gross morphology as described by McDonald (1980).
Ovaries showing the presence of active corpus lutuem were considered to belong to cycling cows, corpus lutuem of pregnancy were identified during sample collection by the presence of a foetus in the uterus. A cow was identified as having abnormal ovarian function when it showed one or more corpus albicans and follicular growth without an active corpus luteum. Animals that had no luteal structure(s) in its ovaries with complete absence of follicles were defined as anoestrus. A cow that had no corpus luteum in any of its ovaries was defined as prepubertal heifer irrespective of the presence of follicles and number and size of the follicles.
One way analysis of variance was used to evaluate the effects of breed on the number of small, medium and large follicles. Data on cycling cows, pregnancy, abnormal ovarian function, anoestrus and prepubertal heifers were used to calculate the prevalence of each with respect to breed.
Of the 1270 cows that were studied, 520 (41.0%) were Red Bororo, 420 (33.0%) were Wadara, while 330 (26.0%) were White Fulani.
Of the 1270 cows, 1120 (88.2%) showed follicular growth on either ovaries, while 150 (11.8%) did not show visible follicles on any of their ovaries. A total of 7830 follicles were identified and measured, out of which 6070 (77.5%) were small follicles, 1620 (20.7%) were medium follicles and 140 (1.79%) were large follicles. Comparison of the three breeds did not reveal any significant difference in the number of small, medium, and large follicles as seen in table 1.
|
Table 1. Effect of breed on follicular size among zebu cows in Northeastern Nigeria |
|||
|
Breed (no. of cows) |
Follicle category (diameter, mean±SEM in mm) |
||
|
Small |
Medium |
Large |
|
|
Red Bororo (520) |
8.58 ± 1.32 |
1.18 ± 0.39 |
0.21 ± 0.10 |
|
Wadara (420) |
11.0 ± 1.61 |
1.36± 0.38 |
0.21 ± 0.07 |
|
White Fulani (330) |
12.0 ± 1.51 |
2.58 ±0.51 |
0.48 ± 0.13 |
|
SEM (standard error of means) |
|||
Prevalence of various functional states of ovaries among the breeds of cows shows that the Red Bororo had the highest prevalence of pregnancy (17.3%); Wadara had the highest abnormal ovarian activity (64.3%) while the White Fulani had the highest cycling cows (12.1%) as seen in table 2.
|
Table 2. Prevalence of various functional states of ovaries among zebu breed of cows in Northeastern Nigeria (n= 1270). |
|||||
|
Breed |
Ovarian activity |
||||
|
Cycling, % |
Pregnant, % |
Abnormal ovarian activity, % |
Anoestrus, % |
Prepubertal heifers, % |
|
|
Red Bororo |
13.5 |
17.3 |
50.0 |
13.5 |
5.77 |
|
Wadara |
14.3 |
9.52 |
64.3 |
9.52 |
2.38 |
|
White Fulani |
21.2 |
6.06 |
45.5 |
12.2 |
15.2 |
The average number of follicles was significantly higher than medium and large follicles with the large follicles having the least mean follicles per ovary. This may be due to the fact that bovine ovaries posses large amounts of small follicular reserve from which graafian follicles are continuously recruited for further development (McDonald 1980).
By comparing follicular growth and luteal structures on the ovaries to different phases of the oestrus cycle, it was deduced that the ovaries that showed a functional corpus luteum were in a state of normal function and that the cows were in a dioestrus phase of the oestrus cycle which is the most lengthy period of the cycle. The presence of small to large sized follicles on the ovaries was a further indication that the wave pattern of follicular turnover was taking place and therefore a state of normal cyclycity (McDonald 1980).The ovaries that were considered as giving abnormal cyclycity although exhibited follicle at various stages of growth could not be classified into any of the four phases of the oestrus cycle namely: metoestrus, dioestrus, proestrus and oestrus based on the luteal structures present on them.
The presence of corpora albicantia at various stages of degeneration was evidence that the cows had had previous oestrus cycles due to the fact that corpora albicantia persist and remain visible as fibrous connective tissue scars on the ovaries for several additional oestrus cycles (McDonald 1980). Metoestrus is the state of early corpus luteum formation characterized by the presence of corpus haemorrhagicum which appears as a blood clot filled follicular cavity, and dioestrus state is characterized by a prominent large functional corpus luteum (Arthur 1974). The implication therefore is that those ovaries were not in either of these two states which make the luteal phase of the estrus cycle. Also preoestrus and oestrus are referred to as the follicular phase of the estrus cycle, in which there is a prominent preovalatory follicle together with a regressing corpus luteum (McDonald 1980). The majority of these ovaries exhibited entirely small and medium follicles, due to these facts, the ovaries were considered to be in a state of abnormal function. The occurrence of abnormal ovarian function has been reported by many workers. (King et al 1976) described various forms of abnormal ovarian function in dairy cows. Such abnormalities included cows that ovulated and formed a functional corpus luteum once followed by a prolonged period of anoestrus with no elevation of progesterone cows that ovulated once or twice followed by prolonged anoestrus with elevated progesterone, and cows that had long irregular cycles and infertility.
Short estrus cycle is also a common abnormality in post partum beef cows where the corpus luteum formed is smaller in size, sub-functional and undergoes premature regression, which renders the cycle shorter than normal (Short et al 1990). Going by these facts, it could be hypothesized that the ovaries classified as being in a state of abnormal cyclicity were possibly obtained from cows that were in a postpartum state, experiencing similar abnormalities and irregularities of cycles like the ones described above, since postpartum period in Bos indicus cows extends to one year or more considering the average calving interval of two years as reported by Voh and Otchere (1989) in Nigerian herds. In addition, some of the cows might be old aged cows that were culled from herds due to decline in reproductive performance, because cows are culled from herds at about 9 to 10 years of age due to decline of productivity (Voh and Otchere 1989). Comparing the ovarian structures and the types of abnormal functions mentioned earlier, some hypothesis could be made about the possible events happening in the animals that made their ovarian activity abnormal. The cows that had ovaries with corpora albicantia and small or medium follicles only, might be experiencing prolonged, irregular oestrus cycle (King et al 1976, Dawuda et al 1988) in which the corpus luteum of dioestrus regressed, but the follicles failed to proceed development to pre-ovulatory stage, perhaps due to suppression of pulsatile reaction of luteinizing hormones (LH) as it occurs in early postpartum cows (Short et al 1990) or in severely malnourished cows (Imakawa et al 1983, Richard et al 1989).
Secondly the cows might be in the processes of initiating postpartum anoestrus after experiencing few oestrus cycles (Dawuda et al 1988) perhaps due to nutritional stress or increased suckling demand (Randel 1990), and in this case, the follicles may be undergoing arrested development. In other situations, the cows might be in the process of reinitiating their normal cyclicity after recovering from suckling stress or under nutrition. In this case the dominant follicle might be in the process of resumption of development to mature stage.
The complete absence of follicular structures observed in the ovaries of some cows was defined as a state of anoestrus due to complete ovarian inactivity because presence of follicles of various sizes is one of the indicators of an active ovary, since visible follicles exist in bovine ovaries right from birth and continue to remain throughout the productive life of the animals (Hopper et al 1993). Furthermore, remnants of luteal structures observed on the ovaries was an affirmation that the cows had experienced successful ovulation and corpus luteum formation prior to complete atresia or disappearance of the follicles which rendered them anoestrus. Other ovaries were classified as prepubertal because no luteal structure could be detected on them despite the presence of follicles. The absence of luteal structures means that the cows had never ovulated as documented by Hopper et al (1993) and coupled with the fact that the size of follicles in the ovaries of infant cows and heifers ranges from 1 to 13mm in diameter (Howe et al 1962) and that the follicles are in the process of continuous development and regression in a pattern similar to that of mature cyclic cows (Hopper et al 1993).
Statistical analysis revealed no significant difference among the Bos indicus cows with respect to different follicle size categories. Also prevalences of different functional state of ovaries earlier classified did not occur in any pattern that could suggest superiority or otherwise of one breed over the other. Red Bororo exhibited the highest prevalence of pregnancy (17.3%) yet the least percentage of cycling animals (13.5%). White Fulani had the highest cycling animals (21.2%) yet the breed exhibited the least pregnancy (16.1%). Wadara had the highest prevalence of abnormal cycling animals (64.3%) nevertheless it recorded the least prevalence of anoestrus cows (9.52%). Previous investigations on breed effects on reproductive activities were focused mainly on comparison between temperate Bos taurus and tropical Bos indicus breeds. For example, Randel (1976) found that Bos indicus cattle secrete less luteinizing hormones during spontaneous surges in the oestrus cycle than the Bos taurus cattle. Rhodes et al (1982) and Sergerson et al (1984) reported that Zebu cattle have smaller corpus luteum and lower progesterone secretion compared to Bos taurus cows. D’occhio et al (1990) demonstrated that during postpartum period, Bos taurus cows showed higher concentration of LH than Zebu cows and higher proportion of the former showed LH pulses during the same postpartum period. Dominguez (1995) detected increase in large follicles in the ovaries of European breed of cows compared to Zebu cross breed cows studied after slaughter and attributed this partially to lower gonadotrophic stimulation as a result of lower LH concentration in Zebu cattle as reported by earlier researchers.
Although this study failed to detect differences in ovarian activities among breeds of Zebu cows, definite conclusion could not be made based on examination of ovarian structures alone, thus, more precise and accurate techniques such as progesterone and gonadotrophic hormone assay or ultrasonographic imaging needs to be employed to monitor the oestrus cycle and activities of ovaries in the cows. Another factor that could have led to this failure of detection of differences among the breeds is that the animals used in this study might have been sent to market or slaughter as a result of old age or fertility problems, or there might have been presence of subclinical disease. These variables were not included and could not be controlled in this study. Only by using single herds for each breed where cows are kept under the same management system with accurate records of health and reproductive activities of each herd, can these factors be eliminated.
In conclusion this study indicated that difference in breed among Zebu cows does not have effect on ovarian activity, however further study using standard herds and more precise techniques such as hormonal assay and ultrasonography may need to be done to further confirm these findings.
Arthur G H 1974 Veterinary reproduction and obstetrics. Bailliére Tindall, London. Pp 14-64
Dawuda P M, Eduvie L O, Esiew K A N and Molokwu E C I 1988 Interval between calving and first observable oestrus in post-partum Bunaji cows. British Veterinary Journal 144(3): 258-261.
D’Occhio M J, Hoskinson R M, Rigby R D G, Trigg T E and Lindsey M J 1990 Suppression of fertility in female cattle with GnRH analogues and an anti-GnRH vaccine. Proceedings of the 22nd Annual Meeting of the Australian Society of Reproduction and Biology, September 24-26, 1990, Perth, Western Australia. Pp 69.
Dominguez M M 1995 Effects of body condition, reproductive status and breed on follicular population and oocyte quality in cows. Theriogenology 43:1405-1418.
Fortune J E 1993 Follicular dynamics during the bovine estrous cycle: A limiting factor in improvement of fertility? Animal Reproduction Science 33:111-125.
Hopper W W, Silox R W, Byerley D L and Kiser T E 1993 Follicular development in prepubertal dairy heifers. Animal Reproduction Science 31:7-12.
Howe G R, Black D L, Foley R C and Black W G 1962 Ovarian activity in prepubertal dairy calves. Journal of Animal Science 21:82-90 http://jas.fass.org/cgi/reprint/21/1/82
Imakawa K, Kittok R J and Kinder J E 1983 The influence of dietary energy intake on progesterone concentration in beef heifers. Journal of Animal Science 56:454-459. http://jas.fass.org/cgi/reprint/56/2/454
King G J, Hurnick J F and Robertson H A 1976 Ovarian function and estrus in dairy cows during early lactation. Journal of Animal Science 42:688-692. http://jas.fass.org/cgi/reprint/42/3/688
Maule P 1990 The cattle of the tropics. Center for tropical Veterinary Medicine, University of Edinburgh, Uk. Pp11-112.
Mcdonald L E 1980 Veterinary endocrinology and reproduction. Lea and Febiger, Philadalphia. Pp 274-398.
Mcdonald I and Low J 1985 Livestock rearing in the tropics. Macmillan, London. Pp. 1-3.
Payne W J A 1990 An introduction to animal husbandry in the tropics. Longman, UK. Pp. 195-421.
Randel R D 1976 LH and ovulation in Brahman, Brahman x Hereford Heifers. Journal of Animal Science (Abstract) 43:300 http://jas.fass.org/cgi/reprint/43/1/209
Randel R D 1990 Nutrition and postpartum rebreeding in cattle. Journal of Animal Science 68: 853-862. http://jas.fass.org/cgi/reprint/68/3/853.pdf
Rhodes R C III, Randel R D and Long C R 1982 Corpus luteum function in the bovine: in vivo and in vitro evidence for both seasonal and breed type effect. Journal of Animal Science 55:159-167 http://jas.fass.org/cgi/reprint/55/1/159.pdf
Richard M W, Wettmann R P and Schoenemann H M 1989 Nutritional anestrus in beef cows: Body weight change, body condition, and luteinizing hormone in serum and ovarian activity. Journal of Animal Science 67:1520-1526 http://jas.fass.org/cgi/reprint/67/6/1520
Sergerson E C, Hansen T R, Libby D W, Randel R D and Getz W R 1984 Ovarian and uterine morphology and function in Angus and Brahman cows. Journal of Animal Science 59:1026-1046 http://jas.fass.org/cgi/reprint/59/4/1026
Short R E, Bellows R A, Staigmiller R B, Berardinelli J G, and Custer E E 1990 Physiological mechanisms controlling anoestrus and infertility in postpartum beef cattle. Journal of Animal Science 68: 799 http://jas.fass.org/cgi/reprint/68/3/799.pdf
Voh A A and Otchere E O 1989 Reproductive performance of zebu cattle under traditional agropastoral management in Northern Nigeria. Animal Reproduction Science 19:191-203.
Voh A A, Oyedipe E O and Buvanendran V 1984 Influence of management and season of breeding on pregnancy rates of zebu cattle in artificial insemination programmes. Tropical Agriculture (Trinidad) 61:265-266.
Received 25 May 2010; Accepted 17 June 2010; Published 1 July 2010