Breeding objectives for pigs in Kenya. I: Bio-economic model development and application to smallholder production systems

Abstract

A deterministic bio-economic model was developed and applied to evaluate biological and economic variables that characterize smallholder pig production systems in Kenya. Two pig production systems were considered namely, semi-intensive (SI) and extensive (EX). The input variables were categorized into biological variables including production and functional traits, nutritional variables, management variables and economic variables. The model factored the various sow physiological systems including gestation, farrowing, lactation, growth and development. The model was developed to evaluate a farrow to finish operation, but the results were customized to account for a farrow to weaner operation for a comparative analysis. The operations were defined as semi-intensive farrow to finish (SIFF), semi-intensive farrow to weaner (SIFW), extensive farrow to finish (EXFF) and extensive farrow to weaner (EXFW). In SI, the profits were the highest at KES. 74,268.20 per sow per year for SIFF against KES. 4026.12 for SIFW. The corresponding profits for EX were KES. 925.25 and KES. 626.73. Feed costs contributed the major part of the total costs accounting for 67.0, 50.7, 60.5 and 44.5 % in the SIFF, SIFW, EXFF and EXFW operations, respectively. The bio-economic model developed could be extended with modifications for use in deriving economic values for breeding goal traits for pigs under smallholder production systems in other parts of the tropics.

Appendix

Calculation of revenues

The sources of revenues are surplus weaners, cull-for-age sows, cull-for-age boars and grower pigs for slaughter. Intangible roles such as source of manure, insurance and prestige of pigs were not included in the model. For simplicity, other variables were introduced which include:

$$ \mathrm{SoWR}=\left(\frac{365}{\mathrm{FI}}\right)\times \mathrm{F}\mathrm{R}\times \mathrm{PrSR} $$

$$ {N}_{\mathrm{w}}{S}_{\mathrm{y}}=\mathrm{SoWR} \times \mathrm{T}\mathrm{N}\mathrm{B} $$

where SoWR is the sow weaning rate (%), FI the farrowing interval, FR the farrowing rate (%), PrSR the preweaning survival rate (%), N _w S _y the number of weaners per sow per year and TNB the total number of piglets born.

Revenue from culled weaners (R _w)

Revenue from surplus weaners was obtained from male and female weaners sold (not used for breeding). Assuming a sex ratio of 1:1, the number of male weaners per sow year (N _mw S _y) attaining selection age is:

$$ {N}_{\mathrm{mw}}{S}_{\mathrm{y}}=0.5\kern0.5em \times {N}_{\mathrm{w}}{S}_{\mathrm{y}} $$

The male weaners culled for sale (N _mw S _y:cull) were calculated as:

$$ {N}_{\mathrm{mw}}{S}_{\mathrm{y}:\mathrm{cull}}={N}_{\mathrm{mw}}{S}_{\mathrm{y}}\kern0.5em \times \kern0.5em \mathrm{males}\ \mathrm{culling}\ \mathrm{rate} $$

The number of weaner gilts per sow per year (N _gw S _y) attaining selection age is equal to:

$$ {N}_{\mathrm{gw}}{S}_{\mathrm{y}}=0.5 \times {N}_{\mathrm{w}}{S}_{\mathrm{y}} $$

and those culled for sale (N _gw S _y:cull) was calculated as:

$$ {N}_{\mathrm{gw}}{S}_{\mathrm{y}:\mathrm{cull}}={N}_{\mathrm{gw}}{S}_{\mathrm{y}}\kern0.75em \times \kern0.75em \mathrm{females}\ \mathrm{culling}\ \mathrm{rate} $$

The replacement gilts per sow per year (R _g S _y) was set equal to the sow replacement rate per year (R _r S _y) since a replacement gilt joining the reproductive stage replaced a cull-for-age sow. The total number of culled weaners (N _w S _y:cull) per sow per year for sale was derived from:

$$ {N}_{\mathrm{w}}{S}_{\mathrm{y}:\mathrm{cull}}={N}_{\mathrm{mw}}{S}_{\mathrm{y}:\mathrm{cull}}+{N}_{\mathrm{gw}}{S}_{\mathrm{y}:\mathrm{cull}} $$

and therefore, the total revenue from culled weaners per sow per year (R _w:cull) was calculated as:

$$ {R}_{\mathrm{w}:\mathrm{cull}} = {N}_{\mathrm{w}}{S}_{\mathrm{y}:\mathrm{cull}}\kern0.75em \times \kern0.5em {P}_{\mathrm{w}\mathrm{eaner}} $$

where P _weaner is the price of weaner.

Revenue from slaughter pigs

Revenue from grower pigs fattened for slaughter (R _g). The number of grower pigs for slaughter per sow per year (N _g S _y) was calculated as:

$$ {N}_{\mathrm{g}}{S}_{\mathrm{y}}=\left({N}_{\mathrm{w}}{S}_{\mathrm{y}}-{N}_{\mathrm{w}}{S}_{\mathrm{y}:\mathrm{cull}}-{N}_{\mathrm{r}}{S}_{\mathrm{y}}\right)\kern0.5em \times \kern0.5em \mathrm{PoSR} $$

where N _r S _y is the number of replacement pigs per sow per year and PoSR the post weaning survival rate. Therefore,

$$ {R}_{\mathrm{g}}={N}_{\mathrm{g}}{S}_{\mathrm{y}} \times \mathrm{L}\mathrm{W}\mathrm{g} \times \mathrm{D}\mathrm{P} \times {P}_{\mathrm{meat}} $$

where LWg is average live weight of grower (kg), DP the dressing percentage and P_meat the price of meat per kg (KES.).

Revenue from culled sows

This includes revenue from cull-for-age sows and was calculated as:

$$ {R}_{\mathrm{s}}={R}_{\mathrm{r}}{S}_{\mathrm{y}}\kern0.5em \times \kern0.5em \mathrm{SoSR}\kern0.5em \times \kern0.5em \mathrm{L}\mathrm{W}\mathrm{s}\kern0.5em \times \kern0.5em \mathrm{D}\mathrm{P}\kern0.5em \times \kern0.5em {P}_{\mathrm{meat}} $$

where SoSR is the sow survival rate and LWs the average live weight of sows at slaughter.

Revenue from culled boars (R _b)

The revenue from culled boars is attained from cull-for-age boars. The number of replacement boars per sow per year (R _b S _y) was derived by:

$$ {R}_{\mathrm{b}}{S}_{\mathrm{y}}={R}_{\mathrm{m}}{S}_{\mathrm{y}}\kern0.5em \times \kern0.5em \mathrm{RoSR}\kern0.5em \times \kern0.5em 0.1 $$

where R _m S _y is the replacement rate for males per sow per year and RoSR the survival rate of replacements to breeding (%). A boar/sow ratio of 1:10 was assumed. Therefore,

$$ {R}_{\mathrm{b}}={R}_{\mathrm{b}}{S}_{\mathrm{y}}\kern0.5em \times \kern0.5em \mathrm{L}\mathrm{W}\mathrm{b}\kern0.5em \times \kern0.5em \mathrm{D}\mathrm{P}\kern0.5em \times \kern0.5em {P}_{\mathrm{meat}} $$

where LWb is average live weight of boars at culling (kg).

Calculation of costs

Costs were incurred in feeds, husbandry, marketing and fixed assets.

Feed costs

Calculation of feed costs was based on the actual feed intake expressed in kg DM. Feed intake was calculated from estimates of the mean intake of energy value of a feed expressed as metabolizable energy (ME). The energy contents in the concentrates and in swill are presented in Table 1. The amounts of energy requirements for the pigs in different physiological and weight categories were those provided by NRC (1998).

Feed intake per animal

Feeding costs for the different classes of pigs (growers, replacement gilts and breeding boars) were derived from the following equation:

$$ {\mathrm{FEED}}_{\mathrm{i}}=\left(\frac{\mathrm{conc}}{{\mathrm{ME}}_{\mathrm{conc}}}+\frac{\mathrm{swi}}{{\mathrm{ME}}_{\mathrm{swi}}}\right)\sum_{\mathrm{i}=1}^{\mathrm{di}}\left({\mathrm{ME}}_{\mathrm{i}}\right) $$

where FEED_i is the feed intake for the animal in category i, conc and swi the proportion of concentrates and swill in the ration, ME_conc and ME_swi the metabolizable energy content (kcal/kg DM) in concentrates and swill, respectively, and d_i the number of days an animal is present in a year.

For the sows, feed intake was derived as:

$$ {\mathrm{FEED}}_{sow}=\left(\frac{\mathrm{conc}}{{\mathrm{ME}}_{\mathrm{conc}}}+\frac{\mathrm{swi}}{{\mathrm{ME}}_{\mathrm{swi}}}\right)\sum_{\mathrm{i}=1}^{\mathrm{di}}\left({\mathrm{ME}}_{\mathrm{mi}}+{\mathrm{ME}}_{g\mathrm{e}}+{\mathrm{ME}}_{\mathrm{lac}}\right) $$

where ME_mi is the metabolizable energy for maintenance, ME_ge the metabolizable energy for gestation and ME_lac the metabolizable energy for lactation.

Accounting for concentrates and swill costs, feed cost (C_F) was then calculated as:

$$ {C}_{\mathrm{F}}=\left(\left(\frac{\mathrm{conc}}{{\mathrm{ME}}_{\mathrm{conc}}}\times {\mathrm{F}\mathrm{EED}}_{\mathrm{i}}\times {P}_{\mathrm{conc}}\right)+\left(\frac{\mathrm{swi}}{{\mathrm{ME}}_{\mathrm{swi}}}\times {\mathrm{F}\mathrm{EED}}_{\mathrm{i}}\times {P}_{\mathrm{swi}}\right)\right)\times {N}_{\mathrm{i}} $$

where N _i is the number of animals in category i, P _conc the price of concentrate and P_swi the price of swill. Piglet feed costs were calculated as:

$$ {C_{\mathrm{F}}}_{\mathrm{p}}={\mathrm{F}\mathrm{EED}}_{\mathrm{p}}\times {N}_{\mathrm{w}}{S}_{\mathrm{y}}\times {P}_{{}_{\mathrm{COMC}}} $$

where FEED_p is the feed intake for piglets from birth to weaning. It was assumed that they consume a total of 8.21 kg of creep feed (Kugonza and Mutetikka 2005).

Husbandry cost

Veterinary costs were those incurred in general drugs and veterinary services, anthelmitics and ectoparasite control for pigs in the different classes. For the piglet class, these costs included iron injection, castration and teeth clipping in the SI. Average husbandry costs (CH_i) per animal were calculated as:

$$ {C}_{{\mathrm{Hi}}_{\mathrm{i}}}={N}_{\mathrm{i}}{\displaystyle \sum_{\mathrm{i}=1}^{\mathrm{d}}\left({\mathrm{lab}}_{\mathrm{i}}+{\mathrm{vet}}_{\mathrm{i}}\right)} $$

where i is the animal class, N the number of animals in category i, d_i the number of days an animal is present in an year, lab the labour costs per animal per year (KES) and vet the veterinary costs per animal per year (KES).

Husbandry costs for piglets from birth to weaning were calculated as:

$$ {\mathrm{C}}_{\mathrm{Hp}}={\mathrm{N}}_{\mathrm{w}}{\mathrm{S}}_{\mathrm{y}} \times \mathrm{w}\mathrm{a} \times \left(\mathrm{lab}+\mathrm{vet}\right) $$

where wa is weaning age. Husbandry costs for growers from weaning to sale age were calculated as:

$$ {C}_{\mathrm{Hg}}={N}_{\mathrm{g}}{S}_{\mathrm{y}} \times \left(\mathrm{s}\mathrm{a}-\mathrm{w}\mathrm{a}\right) \times \left(\mathrm{lab}+\mathrm{vet}\right) $$

where sa is sale age. Husbandry costs for replacement from weaning to age at first farrowing were calculated as:

$$ {C}_{\mathrm{Hrep}}={R}_{\mathrm{r}}{S}_{\mathrm{y}} \times \left(\mathrm{a}\mathrm{f}\mathrm{f}-\mathrm{w}\mathrm{a}\right) \times \left(\mathrm{lab}+\mathrm{vet}\right)+{C}_{\mathrm{r}\mathrm{ep}} $$

where aff is age at first farrowing, and C _rep is the reproduction cost (KES).

Husbandry costs for sow (C _Hs) were calculated including breeding costs per year (C _Hrepro) and general husbandry as:

$$ \begin{array}{c}\hfill {C}_{\mathrm{Hrepro}}=\frac{365}{\mathrm{FI}}\times {C}_{\mathrm{rep}}\hfill \\ {}\hfill {C}_{\mathrm{Hs}}=365\times \left(\mathrm{lab}+\mathrm{vet}\right)+{C}_{\mathrm{Hrepro}}\hfill \end{array} $$

Marketing costs

On per animal basis, transport of live animals to the slaughter house and carcass transport were estimated at KES. 100 each while carcass inspection and slaughter slab fee were set at KES. 300 in the SI. In the EX, transport cost was assumed to be KES. 100, carcass inspection and slaughter slab fee were set at KES. 200.

Marketing costs for surplus weaners (C _Mw) were calculated as:

$$ {C}_{\mathrm{Mw}}={N}_{\mathrm{w}}{S}_{\mathrm{y}:\mathrm{cull}} \times {m}_{\mathrm{w}\mathrm{ean}} $$

where m _wean is the weaner marketing cost per animal (KES) Marketing costs for grower pigs were calculated as:

$$ {C}_{\mathrm{Mg}}={N}_{\mathrm{g}}{S}_{\mathrm{y}}\kern0.5em \times \kern0.5em {m}_{\mathrm{c}} $$

where m _c is the marketing cost per animal (KES) Marketing costs for sows were calculated as:

$$ {C}_{\mathrm{Ms}}={R}_{\mathrm{r}}{S}_{\mathrm{y}}\times \mathrm{SoSR}\times {m}_{\mathrm{c}} $$