herd age and variation in cow disposals

Herd Age and Variation in Cow DisposalsAuthor(s): M. KeaneSource: Irish Journal of Agricultural Economics and Rural Sociology, Vol. 6, No. 2 (1976), pp.213-220Published by: TEAGASC-Agriculture and Food Development AuthorityStable URL: http://www.jstor.org/stable/25556429 .

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HERD AGE AND VARIATION IN COW DISPOSALS

M. Keane

Economics and Rural Welfare Research Centre, 19 Sandymount Avenue, Dublin 4.

ABSTRACT

Disposals of cull cows amount to about 25% annually of total Irish cattle output. Annual disposals have varied considerably as measured by the culling rate, ranging from a maximun culling rate of

25.2% of the herd to a minimum of 11.6% over the past 20 years. Studies have suggested that herd age may be an important factor in explaining variation in cow disposals. The results indicate strongly that herd age, taken in isolation, is unsatisfactory in explaining variation in disposals, and suggest that additional economic variables should be included in any explanatory models.

INTRODUCTION

Net annual disposals of cull cows usually amount to about 25% of total cattle output from Irish farms, with cow slaughterings at licensed export premises, which is by far the

most important component of cow disposals, accounting for 24.7% of estimated net

marketings of cattle over the past 3 years (Appendix Table 1). There is considerable seasonal and annual variation in cow disposals. As regards seasonal variation, cow

slaughterings at meat export premises on a quarterly basis over the last 3 years show that

about one-third of total slaughterings took place in the October-December quarter. This

pattern of slaughterings is consistent with the seasonal production pattern of farm enter

prises based on the cow herd. Milk and calf production is largely timed to coincide with the seasonal pattern of grass growth, with the result that a high proportion of cow

disposals tend to occur at the end of the grazing season, with November normally the

peak month.

Annual disposals are estimated in this report for years beginning June 1, as this follows the quarter with lowest disposals, has the peak month at about the mid-point in the

monthly distribution of disposals, and coincides with an annual livestock enumeration.

The objective is to examine the extent to which estimated variation in herd age structure

213



214 IR. J. AGRIC. ECON. RUR. SOCIOL., VOL. 6, NO. 2,1976

from year to year explains the annual variation in cow disposals. The annual supply of

cull cows in the past has shown major year-to-year fluctuations, which has created con

siderable difficulties for the meat industry, and has resulted in substantial under

employment of industry facilities in some years.

Data sources

As precise data on the components of cow disposals were not obtainable from published

sources a number of estimates were necessary. Net outflow of cows in any period is

defined as slaughterings at licensed export premises, plus slaughterings by butchers for

home consumption, plus mortality, plus exports less imports. While information on the

principal component of disposals, i.e., cow slaughterings at export premises, is readily

available, as are trade statistics, an element of estimation is necessary for cow mortality

and home consumption. However, as these latter elements constitute a small proportion

of total disposals any errors in estimation should not be too important. The inflow of heifers in any period can then be estimated by adjusting net disposals of cows for changes in cow numbers between the beginning and the end of the period. While the inflow of

heifers into the cow herd could alternatively be estimated by taking proportions of

January and June enumerations of in-calf heifer numbers,1 the above method was con

sidered superior.

Annual variation in disposals The total cow herd has expanded by about two-thirds over the past 20 years, from about

1.2 to 2.0 million head (Table 1). Correspondingly the absolute level of cow disposals has also increased considerably. The basic measure of annual disposals is the culling rate,

which relates net disposals in each 12 month period to the number of cows in the herd at the beginning of the period. The average culling rate over the past 20 years is estimated

to be 17.4%, and no significant long term shifts in this rate have occurred, as is evident

in a comparison of the average culling rate over the four years 1971/72-1974/75 (16.3%), with the years 1955/56-1958/59 (16.6%) (Table 1). However, the presence of very considerable year-to-year variation in the culling rate is quite apparent, ranging from the

lowest rate of 11,6% for the year beginning June 1972 to more than double this rate, 25.2%, for the year beginning June 1975.

Importance of age

Two surveys on reasons for culling in recent years have shown that respondents con

sidered age to be an important reason for cow culling (1,2). In addition, age was taken as

the primary explanatory factor accounting for variation in cow disposals in a 1966 study by the Central Statistics Office (3). The hypothesis here is that high culling rates are

associated with comparatively older herds, due to presupposed negative effects of age on cow performance.

1 See (3) page 17.



KEANE: COW DISPOSALS 215

TABLE 1: Cow numbers and culling rate, 1955-1975, '000

Year Cow Cow

beginning numbers disposals Culling rate Estimated Herd age June (1) (2) (2)+(l),% heifer intake factor

1976e 1,973 4.90 1975 2,035 512 25.2 450 5.36

1974 2,151 494 23.0 378 5.91 1973 2,096 329 15.7 384 5.87

1972 1,895 220 11.6 422 5.58 1971 1,782 266 14.9 378 5.51 1970 1,703 279 16.4 358 5.47 1969 1,657 273 16.5 319 5.34 1968 1,607 267 16.6 317 5.26 1967 1,568 308 19.6 347 5.47 1966 1,582 320 20.2 306 5.77 1965 1,547 231 14.9 266 5.62

1964 1,400 171 12.2 318 5.30 1963 1,323 222 16.8 299 5.31 1962 1,309 257 19.6 271 5.40

1961 1,291 214 16.6 232 5.34 1960 1,284 247 19.2 254 5.64

1959 1,272 266 20.9 278 5.94 1958 1,260 206 16.3 218 5.96

1957 1,232 205 16.6 233 6.04 1956 1,187 197 16.6 242 5.98 1955 1,198 202 16.9 191 5.81

e: Preliminary estimates Source: Stat. Bull. C.S.O., Dept. of Agric, Trade Stats, of Ireland, C.S.O.

METHODOLOGY

Direct information on the age distribution of the national herd is quite limited, being obtained mainly from survey data. Consequently, two measures of herd age are estab

lished, based on a series of assumptions.

(i) Herd age factor: This is interpolated from the estimates of annual inflows of heifers into the herd. A simple herd age factor can be derived by estimating the number of successive annual heifer inflows in immediately preceding years required to account for

total cow numbers. Taking the herd size in any year, if the size of the heifer inflow in

the years immediately preceding accounts for a large proportion of the total herd size,

then it is assumed that the herd is relatively young. Estimated herd age factors for the

years 1955-1975 are shown in Table 1. The average herd age factor over the past 21 years

is 5.85, in other words the average number of successive annual heifer inflows in

immediately preceding years required to account for total herd size over the 21-year

period was 5.85. The herd age factor varies from a maximum of 6.04 in 1957 suggesting that the 'oldest' average herd age occurred in 1957, to a minimum of 4.90 in 1975,

indicating that the 1975 herd was the youngest in the past 20 years.



216 IR. J. AGRIC. ECON. RUR. SOCIOL., VOL. 6, NO. 2, 1976

(ii) Age cohorts: The alternative procedure in deriving culling estimates based on herd age is to assume a herd age profile, and apply a set of culling rates for the different lactations.

This procedure, which was adopted in the C.S.O. study (3), requires assumptions on the

rapidity with which culling rates increase with age, and on the maximum age of cows in the herd. Two sets of culling rates per lactation, consistent with an overall rate of

approximately one-sixth of the herd were used in (3). However, a number of other rates

could equally be proposed, and some estimates may also be derived from survey data on

the herd age profile2 (Table 2). The set of culling rates used here is shown in Table 2 Col. 1, and generally lies between the two rates used in (3). The procedure adopted is to

TABLE 2: Assumed culling rates per lactation

Rates used % Derived from (4)

In in (3) present

- Culling

Lactation study A B % of cows rate, %

(1) (2) (3) (4) (5) 1 8.0 7.0 10.0 29.0 44

2 4.0 3.9 3.7 16.6 24 3 5.0 4.0 4.7 12.6 13 4 6.0 4.3 7.3 10.9 17

5 13.0 13.4 13.0 9.0 17

6 25.0 30.6 21.6 7.5 35 7 45.0 62.9 36.0 4.9 20

8 70.0 69.0 62.4 3.9 38 9+ 100.0 100.0 100.0 5.1 38

Source: (3), (4).

apply the assumed set of culling rates to the estimated annual heifer inflows during the

period 1949 to 1955 starting with an 'artificial' herd based on the assumed culling rates for 1948 (see Appendix, Table 2). The herd age structure then becomes successively based on annual heifer inflows, moving away from artificiality, until completely based on annual heifer inflows in 1955. The application of the assumed culling rates to the successive heifer inflows over the period 1955-1974 provides a set of estimates of

expected annual cullings based on herd age structure (Table 3). Two additional adjustments on the original estimates were necessary. Firstly,

differences between the 'expected' cullings based on herd age and the estimated cullings in any year were accounted for by distribution between the lactations in proportion to the fraction of the total herd accounted for by each lactation. Secondly, exceptional 2 There are some reservations concerning the general applicability of the culling rates derived from the

survey data in Table 2 (Col. 5). Firstly, they are based.on a survey taken in 1964 which was an excep tional year in terms of heifer inflow, as is apparent in the breakdown of herd age (Col. 3), with 29.0% of the total herd in the first lactation. Secondly, 1964 followed a period of abnormal cullings due to the tuberculosis eradication scheme which accounted for the removal of abnormally large numbers of cows over the period 1960-1964.



TABLE 3: Total cow numbers by lactation and estimated disposals on basis of herd age ('000)

Year beginning

Culling -

Lactation rate (%) 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964

No. of cows

in herd

1 8 190 191 246 229 218 278 254 232 271 299 2 4 192 174 176 227 211 183 241 226 200 242 3 5 177 184 167 169 216 182 163 218 200 183 4 6 148 168 175 159 161 186 161 147 192 182 5 13 169 139 157 165 149 137 163 144 128 174 6 25 160 147 121 137 143 121 114 141 121 111 7 45 96 120 111 91 103 106 93 92 110 97 8 70 52 52 66 61 50 64 69 67 63 77 ? 9 100 15 16 20 18 25 32 42 38 38 35 >

Z

Total cow numbers 1,198 1,187 1,232 1,260 1,272 1,284 1,291 1,309 1,323 1,400 ?

Expected disposals 197 203 208 205 322 308 300 338 298 236 O Actual disposals 202 197 205 205 266 247 214 257 222 171 ^

O

Year beginning June 55

Culling - g

Lactation rate (%) 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 ?

_ > - r

No. of cows in herd ?? 1 8 318 266 306 347 317 329 348 378 422 384 378 2 4 283 295 237 268 310 284 297 318 357 388 335 3 5 235 273 279 222 253 294 270 284 308 343 363 4 6 177 224 254 258 207 237 276 255 273 292 316

5 13 175 167 205 231 237 192 220 259 243 256 264 6 25 159 154 137 164 190 198 162 189 232 211 203

7 45 92 125 101 85 108 130 140 120 152 173 127

8 70 67 59 47 32 33 46 61 74 78 82 49

9 100 41 24 2 2 3 8 16 33 21

Total cow numbers 1,547 1,582 1,568 1,607 1,657 1,703 1,782 1,895 2,096 2,151 2,035

Expected disposals 248 238 308 197 217 236 251 274 325 323 257 Actual disposals 231 320 204 267 273 279 268 220 329 494

Herd components may not add to totals due to rounding



218 IR. J. AGRIC. ECON. RUR. SOCIOL., VOL. 6, NO. 2, 1976

culling rates occurred over the period 1960-64 due to the bovine T.B. eradication scheme,

with the number of 'reactors' amounting to about 100,000 per annum in this period. It

was assumed that the number of reactors in this period was derived directly in proportion to the fraction of the total herd accounted for by each lactation.

RESULTS

The relationships between the culling rate and the herd age factor, and between estimated

disposals and expected disposals using the age cohort method, are outlined in equations 1

and 2, and are shown graphically in Figs. 1 and 2. In the case of equation 1 and Fig. 1, a

direct relationship is hypothesised between the herd age factor and the culling rate, i.e. a high herd age factor is assumed to be associated with an older herd leading to a higher culling rate, and vice versa. In the case of equation 2 and Fig. 2, a direct relationship

between expected and estimated disposals is hypothesised. The notation for the variables in the equations is:

CULRAT = culling rate

HRAGFC = herd age factor EXPCUL =

expected disposals (age cohort method)

Herd age factor 1_ ^ 30-u-x _ r6 ?

a> Culling rate^^ \/ o

i io- y

-4^

3 -? Of i i?i?i?i?i?i?i?i?r?i?i i i i?i i i i i L3

*

Fig. 1

8 600n g Estimated disposals ,_--.

j2 400- Expected disposals /

& 200- ^^^^^^^r^^..<r ""

? 0 t i i i \ i i > i i t i i i i i i i i i n

<S 1955 59 63 67 71 75 Year

Fig. 2

Fig. 1 (top): Culling rate and herd age factor

Fig. 2: Estimated and expected cow disposals



KEANE: COW DISPOSALS 219

ESTCUL = estimated disposals.

Equn (1): CULRAT = 8.43 + 1.51 HRAGFC, R2 = 0.01, d = 0.90

(2.88) Equn (2): ESTCUL = 108.75+0.62 EXPCUL, R2 = 0.12, d = 0.43

(0.39)

The models are assumed to be linear in form in both cases. In both equations, the

exceedingly low R2, and the fact that the coefficients for the independent variables are

non-significant, strongly indicates that the variables representing herd age, taken in

isolation, are quite unsatisfactory in explaining variation in cow disposals. Furthermore,

the Durbin Watson d statistic leads to rejection of the hypothesis of random disturbances at the 5% level, indicating that the models are incorrectly specified and further relevant

independent variables are omitted. These results are also apparent from the graphical

presentation of the hypothesised relationships in Figs. 1 and 2.

CONCLUSIONS

It appears clear from the above results that farmers are not tied rigidly to disposal of cows

on the basis of age, but rather are free to respond to various economic variables. Based on

the theory of supply response it might be postulated that changes in the value of the

output from cows, or changes in the price of cows for disposal, may stimulate farmers to

sell differing proportions of their herd from year to year. In reconciling these conclusions

with farm survey results indicating that age was of major importance in determining cow

disposals, it can be argued firstly that a certain minimum proportion of the herd will almost unavoidably be disposed of each year, due to the occurrence of afflictions,

perhaps associated with age, which would make retention totally uneconomic. For

example, at least 11.6% of the herd has been disposed of each year since 1955. Secondly, while a farmer may be favourably disposed to the disposal of an older cow, it is likely that in many cases flexibility can be maintained in the light of economic circumstances,

such that if returns from milk and calves were particularly favourable the decision could

be postponed for a year or longer. Hence the economic variables may be of primary

importance in explaining variation in cow disposals.

REFERENCES

1. Cunningham, E. P., Shannon, M., Fallon, T. J. and O'Byrne, T. M., 'Why cows leave home', Fm Fd

Res. 7: 46, 1976. 2. Keane, M., 'Estimating cull cow supplies', Fm Fd Res. 4:31,1973. 3. Farm Bulletin, Department of Agriculture, July 1966.

4. Cunningham, E. P., 'Components of variation in dairy cow production records', Ir. J. agric. Res.

11: 1,1972.

Received October 1976



220 IR. J. AGRIC. ECON. RUR. SOCIOL., VOL. 6, NO. 2,1976

APPENDIX

TABLE 1: Summary of cattle disposals 1973-1975, '000 head

1973 1974 1975

Live exports 430 447 642

Slaughterings at meat export premises Cows, annual 239 413 600

Cows, % by quarter January-March 21 26 24 April-June 18 18 15 July-September 26 24 27

October-December 35 32 34

Prime cattle 401 649 750

Total cattle 640 1,062 1,350

Total beef exports 645 1,047 1,340 Total live and beef exports 1,075 1,494 1,982

Imports 98 93 100 Net exports 977 1,401 1,882 Slaughterings for home market 227 287 290 Net marketings 1,204 1,688 2,172

Source: Annual Review of Livestock and Meat Industry 1975, CBF Bulletin.

TABLE 2: Derivation of 1955 herd from 1949 'artificial* herd1

Year beginning June *000

Culling -

Lactation rate (%) 1949 1950 1951 1952 1953 1954 1955

No. of cows in herd

1 8 196 244 220 179 201 209 190 2 4 180 179 219 199 163 185 192 3 5 173 172 170 208 190 156 111 4 6 164 164 161 160 197 180 148 5 13 155 153 152 149 149 185 169 6 25 137 132 128 128 128 129 160 7 45 101 99 90 89 92 96 96 8 70 56 52 43 41 45 51 52 9+ 100 14 14 6 6 9 13 15

Cow disposals 211 240 209 186 179 196 202

Total cows 1,176 1,209 1,189 1,159 1,174 1,204 1,198

1 Based on the successive introduction of actual annual heifer inflows.



herd age and variation in cow disposals

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